Draft:Production of The Exorcist

The 1973 horror film The Exorcist was very challenging to make. It went over budget, with 200 days of principal photography far beyond its original schedule. Filming took place in environments ranging from a hot desert to an operating room to a heavily refrigerated bedroom set. Most of the sets had to be rebuilt early in production after being destroyed in a freak fire, and a number of cast and crew either suffered serious injuries or died during filming or shortly afterwards, leading to a belief that the film, and its many sequels, are cursed.

Difficulties began in preproduction. William Peter Blatty, who had written the bestselling 1970 source novel, managed to retain the rights to produce the screen adaptation he had already written. But after several major directors of the time turned the project down, he found it very difficult to find one he was comfortable with until William Friedkin, fresh from winning the Academy Award for Best Director for The French Connection, signed on after reading the novel.

Casting was problematic already. Several A-list actresses who were approached for the part of Chris MacNeil who either turned the part down or had demands which could not be accommodated, leaving Ellen Burstyn, to take the role. Friedkin was considering casting an older actress to play the challenging part of Regan McNeil, Chris's demonically possessed daughter, which required sexually explicit and shocking behavior that adult women doubled for, until Linda Blair auditioned. Jason Miller, the writer of a hit play who had never acted in films, was cast as the male lead, Father Alex Karras, over Stacy Keach. Warner Bros., the studio, was apprehensive about making a major and controversial film with three actors not widely known to audiences, especially after Friedkin rejected Marlon Brando for the supporting role of Father Lankaster Merrin, ultimately played by Max von Sydow.

The film's groundbreaking special effects, including a famous scene where Regan's head appears to completely spin around, were largely done live on camera. Friedkin also praised the work of makeup artist Dick Smith in creating the look of the possessed Regan and the aged Merrin. Cinematographer Owen Roizman has received praise for another famous scene, where Father Merrin arrives at the MacNeils' Georgetown home on a foggy evening.

Novel
Aspects of Blatty's novel were inspired by the 1949 exorcism performed on a boy known as "Roland Doe" or "Robbie Mannheim" by the Jesuit priest William S. Bowdern. The novel changed several details of the case, such as the sex and age of the allegedly possessed victim. Harper & Row, believing the book would sell well, published it and sent Blatty on a 26-city book tour. But despite enthusiastic reviews, sales were not as strong as the publisher had hoped; at one point the bookstore cancelled Blatty's appearance because, it told him, so few copies had been sold that it was remaindering the unsold ones back to the publisher. Harper was about to give up and had even, according to Blatty, treated him to a farewell lunch, when an opportunity to appear on The Dick Cavett Show came up after one guest canceled and the other, actor Robert Shaw, was too drunk to go on. Cavett was uninterested in the supernatural, but let Blatty talk about The Exorcist at length, captivating the audience with discussions of whether the devil existed. Soon afterwards the novel was atop the New York Times best seller list.

Despite Blatty's previous experience working in Hollywood as a writer for Blake Edwards' films, film studios had generally been uninterested in adapting The Exorcist before its publication. Lew Grade made a modest offer for the rights that Blatty said later he would have accepted due to his difficult financial circumstances, but for his requirement that he produce. Shirley MacLaine, a friend of Blatty's on whom he had based the Chris McNeil character in the novel, to the point of using some things she had said in the past as dialogue, had been interested. But Blatty refused to back down on producing, so Grade and MacLaine moved on to other projects.

Paul Monash, producer of Butch Cassidy and the Sundance Kid, then expressed interest. He and Blatty reached a $400,000 ($ in ) deal that gave Monash six months to get a studio to commit to filming The Exorcist. He soon secured a deal with Warner Bros. for $641,000. Blatty recalled that studio head John Calley had been reading the book at his home, alone, in his bedroom, and found his dog unusually unwilling to join him on the bed. He tried to drag the dog onto the bed but the animal resisted vigorously. When he finally succeeded, he found the book was hot to the touch.

Blatty and Monash had agreed to be co-producers. But Monash wanted changes to the story Blatty opposed, such as setting it somewhere else, making Kinderman less colorful and Chris something other than a film actress, getting rid of the prologue and even Father Merrin's character. Hearing rumors that Monash was planning something behind his back, Blatty was able to sneak into his office at Warners and surreptitiously copy some papers from Monash's files that lent credence to those rumors. When he shared those papers with the studio, he became the film's sole producer.

Writing
Blatty's screenplay follows the plot of his novel closely, but narrows the story's focus. Subplots like the desecration of the churches (and the relationship between Karras and Kinderman that develops from the latter's investigation), Karras's efforts to get the Church bureaucracy to approve the exorcism, and the ongoing medical investigations of Regan's condition, are acknowledged in the film but to a much lesser degree than in the novel. Similarly, characters such as Chris's household staff, Dennings, and Regan's father, play a smaller role, and the overall time frame of the plot is condensed.

"I compressed the first third of my book into only 33 pages" of script, Blatty wrote later. He eliminated the subplot with Karl's daughter Elvira, despite its reinforcement of Merrin's belief that some good will always eventually come of any evil since at the end of the novel she goes into treatment for her heroin addiction. "I hated to do that", he admitted. "But there simply wasn't time and the subplot had to go." For the same reason he greatly reduced the suggestions that Karras was responsible for both Denning's death and the desecrations in the chapel, hints he felt many readers had missed anyway.

Some scenes, particularly those with sexual content, were toned down for the movie since an actress of approximately Regan's age was expected to be playing the part. The scene where Regan masturbates with a crucifix was, in the book, more prolonged and explicit, with Regan seriously injuring herself yet attaining orgasm. The film also excludes the detail from the book that when possessed, Regan experiences constant diarrhea, requiring that she wear a diaper and giving her room a strong odor. One of the film's religious advisers, Father John Nicola, who had opposed including both the crucifix scene and the desecration, nevertheless advised that the language used by Pazuzu when possessing Regan should be even more profane than it was in the book, to an extent he considered more realistic; it was changed accordingly.

Blatty also made the screenplay unambiguous about Regan's condition. In his novel every symptom and behavior she exhibits that might indicate possession is counterbalanced with a reference to an actual case where the same phenomena were found to have natural, scientific causes. Beyond Karras' initial professional skepticism, that perspective is absent from the film.

When Friedkin came onto the project as director, Blatty expected that, as directors usually do, he would propose some changes to the story. But Friedkin did not, insisting on following the novel closely. According to Blatty, Friedkin even asked him, in one scene, to restore some slight changes to his dialogue to what it had originally been in the book.

Casting
The film's lead roles, particularly Regan, were not easily cast. Although many major stars of the era were considered for the role, with Stacy Keach signed to play Father Karras at one point, Blatty and Friedkin ultimately went with less well-known actors, to the consternation of the studio.

Chris and Father Karras
The studio wanted Marlon Brando for the role of Lankester Merrin. Friedkin did not want to make a "Brando movie" and refused. Jack Nicholson was considered for Karras, and Paul Newman interested, before Blatty hired Stacy Keach.

Three A-list actresses of the time were considered for Chris. Audrey Hepburn said she would take the role but only if the movie could be shot in Rome, where she was living. That posed too many problems, so Friedkin looked next to Anne Bancroft. She was also willing but only if production could start after she gave birth; Friedkin could not wait nine months. Jane Fonda, next on the list, purportedly derided the film and turned it down.

Blatty suggested MacLaine for the part, but Friedkin was hesitant, given her lead role in another possession film, The Possession of Joel Delaney, two years before. After meeting Carol Burnett at a party, Friedkin believed she had the range beyond her comic television persona, and Blatty agreed, but the studio was not so eager to have her in the role. Ellen Burstyn received the part after she phoned Friedkin and emphatically stated that she was "destined" to play Chris, discussing her own Catholic upbringing and later rejection of it. Studio head Ted Ashley vigorously opposed casting her, not only telling Friedkin that he would do so over his dead body, but dramatizing that opposition by making Friedkin walk over him as he lay on the floor, then grabbing the director's leg and telling him he would come back from the dead if necessary to keep Friedkin from doing so. However, no other alternatives emerged, and Ashley relented.

With Burstyn now set in the part, Friedkin received a surprise return call from Jason Miller. The two had briefly spoken after a performance of Miller's play That Championship Season about the lapsed Catholicism in it, as background for the film. Miller, who had not previously read the novel despite being aware of its popularity, had read a copy of the novel Friedkin left him, and told the director "[Karras] is me". Miller had had a Catholic education, and had studied to be a Jesuit priest himself for three years at Catholic University of America (also in Washington) until experiencing a spiritual crisis, as Karras does early in the story. Friedkin thanked him for his interest but told him Keach had already been signed.

Miller, who had done some stage acting but had never been in a film, asked to be given a screen test. Friedkin had the playwright and Burstyn do the scene where Chris tells Karras she thinks Regan might be possessed. Afterwards, he had Burstyn interview Miller about his life with the camera focusing on him from over her shoulder, and finally asked Miller to say Mass as if for the first time, with a grapefruit can as the chalice, Ritz crackers as the host and a copy of the novel standing in for the Bible. "I felt like I was in a dark universe", Miller recalled. Burstyn felt Miller was too short for the part, unlike her boyfriend at the time, whom Friedkin had auditioned but passed on. The director felt the test was promising but, after viewing the footage the next morning, realized Miller's "dark good looks, haunted eyes, quiet intensity, and low, compassionate voice", qualities which to him evoked John Garfield, were exactly what the part needed. He had "a kind of amateur humanity few established actors can get to" Friedkin said later, recalling Warner's had been so impressed that it offered Miller a four-picture deal which he turned down to continue playwriting. The studio bought out Keach's contract.

Regan
Directors considered for the project were skeptical that a young actress could carry the film. Mike Nichols had turned down The Exorcist specifically because he did not believe a 12-year-old girl who could play the very stressful part could be found. The first actresses considered had been in other successful films and television series. Pamelyn Ferdin, a veteran of science fiction and supernatural drama, was ultimately turned down as too familiar. Denise Nickerson, who had appeared in two roles on the horror-soap opera Dark Shadows and played Violet Beauregarde in Willy Wonka & the Chocolate Factory, said in later interviews her family found the script too dark for her. Janet Leigh would not let her daughter, Jamie Lee Curtis, audition.

Friedkin had interviewed girls as old as 16 who looked young enough to play Regan, but found none. Then Elinore Blair came in unannounced with her daughter Linda; her agency had not sent her for the part, but she had previously met with Warners' casting department. Both impressed Friedkin. Elinore was not a typical stage mother, and Linda's credits were primarily in modeling and a single soap opera role. "[S]mart but not precocious. Cute but not beautiful. A normal, happy 12-year-old girl", Friedkin later recalled.

With Linda having the qualities Friedkin was looking for, he wanted to see if she could handle the material. He asked if she knew what The Exorcist was about; she told him she had read the book. "[I]t's about a little girl who gets possessed by the devil and does a whole bunch of bad things." Friedkin then asked her what sort of bad things she meant. "[S]he pushes a man out of her bedroom window and she hits her mother across the face and she masturbates with a crucifix." Friedkin then asked Linda if she knew what masturbation meant. "It's like jerking off, isn't it?", and she giggled a little bit. "Have you ever done that?" he asked. "Sure; haven't you?" she responded.

She was cast after tests with Burstyn; Friedkin wanted to keep that level of spontaneity on set. "After all these difficult scenes she'd tiptoe around and giggle, after every bit", Blatty recalled. "It was all a big funhouse ride for her. She was disturbed only one time, and that was when her pet mouse died." After filming, Friedkin had similar praise: "She is the most totally pulled together, stable, mature young person I've ever met. The whole thing was a game to her." Of the 500 actresses he said he saw audition, "there wasn't one other I would have considered."

Friedkin showed the sound editors a Hieronymus Bosch painting from a book and said that was how the possessed Regan's voice should sound. They began by using Blair's voice electronically treated, for the demon's dialogue. He felt this worked fine in some places, but the scenes with the demon confronting the two priests lacked the dramatic power required. So instead he cast Mercedes McCambridge, an experienced voice actress and Oscar winner, as the demon's voice, due to the androgynous qualities of her voice. After she had consumed whiskey, raw eggs and smoked several cigarettes, McCambridge recorded her lines strapped into a chair. "The most curious things would happen in her throat", Friedkin recalled. "Double and triple sounds, wheezing sounds very much akin to what you would imagine a person inhabited by various demons would sound like." After filming, Warners did not credit her, until Screen Actors Guild arbitration. While it concluded quickly enough that McCambridge's name was included in the credits on all but the first 30 prints, it prevented the release of a soundtrack album that was to include excerpts of dialogue.

Actress Eileen Dietz, 15 years Blair's senior and her lighting double, stood in for her in the crucifix scene, the fistfight with Father Karras, the vomiting,  and others that were too violent or disturbing for Blair to perform. She also appears as the face of Pazuzu. Friedkin gave her no notes, telling her to play the possessed Regan as "a primal force of malevolence ... I wasn't playing a little girl, I was playing the demon that possessed a little girl".

Reportedly Warners had forced Friedkin to hire her; he in turn used her only when absolutely necessary. Blair, who recalls Friedkin telling her the film would not succeed if she was not in as many shots as possible, estimates that Dietz's total screen time amounts to 17 seconds. Dietz, angry that her contribution to the film had been minimized, claimed in the media to have done all the possession scenes. Warners ultimately measured her screen presence at 28.25 seconds.

Supporting roles
The film's supporting roles were cast more quickly. A Philippe Halsman photograph of Pierre Teilhard de Chardin, one of Blatty's inspirations for Father Merrin, inspired Friedkin to cast Max von Sydow instead of Paul Scofield, who Blatty had wanted. "He portrays great spiritual quality on film." At a play, Blatty and Friedkin ran into Lee J. Cobb, who was cast as Lt. Kinderman.

Two priests were cast. Father William O'Malley had become acquainted with Blatty through his criticism of the novel. After Blatty introduced him to Friedkin, they cast him as Father Dyer, a character O'Malley had considered clichéd in the novel, after he had gotten permission from his provincial, who granted it because he believed the movie had something to say about faith. The Rev. Thomas Bermingham, the Georgetown professor who assigned Blatty to do the research on demonic possession that later informed the novel, took the role of the university president.

Cast sheets in The Hollywood Reporter and a Warners press release, list British director J. Lee Thompson as a member of the cast early in production. It was suggested that he would be playing Dennings, whom Shirley MacLaine says was based on him as he had directed the 1965 film John Goldfarb, Please Come Home!, which Blatty had adapted for the screen from his novel, but Jack MacGowran got the role instead. A later cast listing adds Mary Boylan and The Rev. John Nicola, one of the film's technical advisors, in small roles. Greek actor Titos Vandis, cast as Karras's uncle, covered his face with a hat, as Friedkin felt audiences would associate him with his role in the recent Woody Allen film Everything You Always Wanted to Know About Sex* (*But Were Afraid to Ask). Friedkin reportedly cast Vasiliki Maliaros as Karras's mother after encountering her in a Greek restaurant.

Direction
Warners had approached Arthur Penn, Stanley Kubrick, and Mike Nichols to direct; for various reasons they were turned down or turned it down. Blatty approached Peter Bogdanovich with a copy of the book he had written a personal plea in but the director saw the material as indistinguishable from other horror films. Another director contacted, John Boorman, who later directed the sequel, Exorcist II: The Heretic, not only turned the film down but advised Warners against making it. Blatty recalled in 2015 that one director wanted to set the film in Salem, Massachusetts, which he rejected because he considered the contrast between the worldly nature of the capital and the supernatural aspects of the plot to be essential to the story.

The studio finally hired Mark Rydell to direct, but Blatty insisted on Friedkin as he had been impressed by The French Connection. He also knew Friedkin, who had critiqued his Darling Lili screenplay over lunch before production. Blatty also appreciated that at a meeting with Edwards, Friedkin had been extremely frank about the shortcomings of a Peter Gunn script, to the extent of costing himself the directing job.

Blatty saw Friedkin as "a director who can bring the look of documentary realism to this incredible story, and ... a guy who is never going to lie to me." The studio was still resistant, until The French Connection was released to commercial success and a Best Picture Academy Award. One night while doing his press tour for that film, Friedkin began reading a copy of the novel Blatty had sent. After the first 20 pages he canceled his dinner plans and finished the book. The issues that had given other directors pause did not bother Friedkin: "I was so overwhelmed by the power of this story, and I didn't stop to think about the problems involved with making it."

"The pacing is deliberate, and I wanted it to happen slowly because the story, as it affected the real people who inspired it, took place in just that way", Friedkin said in 2015. "I felt we had to go through all of that. You had to see the symptoms. You had to see the treatment that was given out by internal medicine and by psychiatry, and to see that it all had been tried and failed." To emphasize the clash of the forces of light and darkness, Friedkin planned the film to begin with the very bright outdoor scenes in Iraq, and then contrasting them with the dim interiors of the MacNeil home in Georgetown later.

Friedkin took inspiration for his storytelling from British playwright Harold Pinter's The Birthday Party, whose 1968 film adaptation he had directed after being impressed with the play. He was struck by how Pinter never completely explained why the play's protagonist is being hunted and questioned; Pinter had told him that, in turn, he had been inspired by how Ernest Hemingway's short story "The Killers" never explains why its titular hit men have been assigned to kill their target. Pinter's play "prepared me for an ambiguous kind of storytelling as being more powerful than nailing things on the nose."

Early in production, Blatty fired Friedkin when he challenged him after they clashed over what the director felt was Blatty's mishandling of Burstyn's request that a limousine pick her up from the airport, a policy Friedkin himself had instituted. Blatty assumed the two would soon reconcile. Two days later, according to Blatty, he was summoned to a meeting with not only Friedkin but his agent and seven studio lawyers who told Blatty he could not fire the director. After that, Blatty recalled to Peter Biskind, he informed the studio he could no longer have any responsibility for controlling the costs. He and Friedkin reconciled and got along well for the rest of the picture. Production costs soon exceeded the film's initial $4.2 million ($ in modern dollars) budget.

Friedkin went to great lengths manipulating actors to get the reactions he wanted. Late in the film, Friedkin was unsatisfied with O'Malley's performance as Dyer ministers to the dying Karras at the end of the film, telling him he was doing it "by the numbers". O'Malley protested that it was 2:30 a.m. and he had just administered last rites to his friend for the 15th time. Friedkin then asked if O'Malley trusted him; when the priest said yes, Friedkin slapped him hard across the face to generate a deeply solemn yet literally shaken reaction for the scene, offending the many Catholic crew members on set. "It was beyond what anyone needs to do to make a movie," Burstyn said in 2019.

He also fired blanks without warning to elicit shock from Miller for a take, angering the actor as Miller did not believe he needed the external stimulus to deliver a convincing performance. Dietz recalls him also doing this during the scene where Regan assaults the doctors who have come to see her. Friedkin also told Miller that the vomit, porridge colored to resemble pea soup and pumped through a hidden tube, would hit him in the chest during the projectile vomiting scene, and rehearsed it that way. But when filmed, the soup hit his face, resulting in his disgusted reaction.

Friedkin also used smell to manipulate the actors, Dietz recalls. Since the demon's presence was, in the book, accompanied by the stench of Regan's near-continuous diarrhea, to ensure an equally distasteful odor on set the director would hide rotten meat or eggs somewhere on set. While it worked initially, "[t]he problem was the crew and the cast all got sick so we had to stop shooting", Dietz said.

Crewmembers found Friedkin demanding and sometimes difficult to work with. One of the first shots, when production began in New York, was of bacon being cooked on a griddle. It begins as a close-up and then pulls back. A wall had been built opposite the stove, leaving almost no space for the dolly, so Friedkin halted shooting while it was removed. Afterward, he did not like the way the bacon curled while cooking, so the prop master was sent to look for preservative-free bacon, difficult to find at the time, further delaying the scene. Another crewmember recalls returning after three days of sick leave to find Friedkin still shooting the same scene.

Dietz recalls shooting taking so long because Friedkin reshot most of the film. Even scenes that had been difficult to stage and film the first time, such as Regan's bed shaking, were redone. "People were literally placing bets on what he would re-shoot next." Friedkin also fired and rehired crew regularly. One crewmember recalls seeing the director shake hands warmly with someone, and then seconds later tell a second person to "get this guy outta here". This mercurial behavior led the crew to call him "Wacky Willy".

Cinematography
After working with Friedkin as director of photography on The French Connection, Owen Roizman took the same position on The Exorcist. He was in charge of filming every scene in the film save those in the Iraqi prologue, shot by Billy Williams. In a 1974 interview with American Cinematographer, the magazine of the American Society of Cinematographers, Roizman discussed The Exorcist at length.

"[H]e figured that since we'd done so well the last time, maybe we could do it again", Roizman said, recalling how Friedkin had gotten him to work on The Exorcist. They agreed that, like their earlier film, they wanted the next one to look as if shot with available light. But this time they would eschew Connection's documentary look. The MacNeil house was, unlike house interiors in horror films such as Psycho, designed to look normal and inviting. "What we tried to do, by means of the lighting, was to give it a kind of ominous feeling—as if some lurking, mysterious thing were hanging over it. That's about as far as we went with photographic style."

While much of the filming took place in the set for Regan's bedroom, there were some other parts of the house set that presented challenges when filming. Roizman said the 7 ft ceiling of the basement set left no room for conventional lighting setups. "There was really no place at all to put lights and, in doing any sort of pan around or dolly shot, we would have been fighting ourselves had we tried to use conventional lighting units." But the crew was able to make those shots work by replacing the ceiling's practical light bulbs with photofloods.

"Friedkin demanded complete realism", Roizman recalled. "He wanted to see pictures with glass in them, mirrors on the walls and all of the other highly reflective surfaces you would naturally find in a house, we never tried to cover anything up, as we would normally do for expedience in shooting." This realism meant that the kitchen set, with much stainless steel and glass, was "virtually impossible" to light beyond the practical ceiling fixtures and whatever other lights they could manage to sneak in and hide. "[W]e'd walk in, hit the switch and shoot—through not much choice."

One shot early in the film seemed simple when seen but, according to Roizman, required intense preparation and rehearsal. In it, Sharon greets the doctors and escorts them upstairs to Regan's room. The camera starts the scene at the top of the staircase, follows the actors from there as they walk towards it, tracks backward in front of them as they walk up to it towards the room around two corners and then turns again to let the actors pass, pan right and follow Karen as she goes to the door. It was necessary first to build a specialized chair for the camera operator on a track along the ceiling, then the grips had to move the camera in sync with the actors without causing any bumps. It was then necessary to light the scene while avoiding any crew shadows, which they did with photofloods and striplights through overhead muslin. "If I were to do that shot over again, I would probably underexpose a bit more to accentuate the shadows, but, all in all, the shot worked very well" said Roizman

Filming and locations
The film's opening sequences were filmed in and near the city of Mosul, Iraq, a country with which the U.S. did not then have diplomatic relations. It was also experiencing civil unrest that later grew into civil war; Warners feared that Friedkin and his crew might not be able to return. Friedkin negotiated filming arrangements directly with the local officials of the ruling Ba'ath Party. He was allowed to shoot only on the condition that he hire lots of local workers as crew and teach some classes in filmmaking to interested residents, primarily in how to create and use fake blood. The archaeological dig site shown is ancient Hatra, south of Mosul. Temperatures during the days filming took place reached 130 °F, limiting shooting to the early mornings and evenings. After shooting William Kaplan, the film's production supervisor, was held under armed guard in Baghdad as a check from Warners bounced. Although the film is set in Washington, D.C., many interior scenes were shot in various parts of New York City. The MacNeil residence interiors were filmed at CECO Studios in Manhattan. U.S. Senator Lloyd Bentsen's million-dollar fee for the use of his house's interiors was too high.

Principal photography began in mid-August 1972 with Karras's confrontation with his uncle over his mother's care, shot at Goldwater Memorial Hospital on Roosevelt Island in the East River between Manhattan and Queens; the scenes with Karras's mother in the hospital were filmed at Bellevue. The scene where Father Karras listens to the tapes of Regan's dialogue was filmed in the basement of Keating Hall at Fordham University in the Bronx, where O'Malley, who plays Dyer, was an assistant professor of theology.

The exterior of the MacNeil house was a family home on 36th and Prospect in Washington, on the former site of E. D. E. N. Southworth's residence. A mansard roof was added to account for the scene in which Chris investigates the scratching noises in the attic. The stairs were padded with half-inch-thick (0.5 in) rubber to film Karras's death. Because the house he falls from was set back slightly from the steps, the crew built an eastward extension with a false front to film the scene. The stuntman tumbled down the stairs twice. Georgetown University students charged people around $5 each to watch the stunt from the rooftops.

The interior of Karras' room at Georgetown was a meticulous reconstruction of theology professor Father Thomas M. King's "corridor Jesuit" room in New North Hall. King's room was photographed by production staff after a visit by Blatty, a Georgetown graduate, and Friedkin. Back in New York, every element of King's room, including posters and books, was recreated, including a poster of Pierre Teilhard de Chardin, a theologian on whom Merrin was loosely based. Georgetown was paid a thousand dollars ($0 in ) per day of filming. Locations on campus included both exteriors such as Burstyn's first scene, shot on the steps of the Flemish Romanesque Healy Hall, and interiors such as the defilement of the statue of the Virgin Mary in Dahlgren Chapel, and the Archbishop's office, actually the office of the university's president. One scene was filmed in The Tombs, a student hangout across from the steps. Roizman recalls the scenes in the chapel as the hardest interior to light after the house sets. In order to give it the same available-light look as the house interiors for an establishing shot that included the stained glass windows, it was necessary to rig it with 225-amp "Brute" arc lights on 30 ft parallel mounts. "It was backbreaking work ... but the results were quite pleasing."

Exorcism scenes
The scenes where Merrin and Karras perform the exorcism were challenging to film. Following the novel, Friedkin wanted the bedroom set to be cold, cold enough to see the actors' breath. A $50,000 ($ in modern dollars) refrigeration system, which Friedkin described as powerful enough for a restaurant, was installed that could lower the temperature within to -20 F, after running all night,  cold enough that a thin layer of snow fell within it one humid morning, so the characters' breath would be visible. Since the set lighting warmed the air, it could only remain cold enough to film for three minutes at a time; after 90 minutes the lights would warm the room above freezing, requiring filming to stop until it could be recooled. The refrigeration broke down frequently, and Friedkin was only able to complete five shots each day. The complete scene thus took a month to film, in continuity, the order it was written in the script.

Originally it was hoped that the room would not have to be chilled that much. But while the actors' breath was visible at just below freezing, the set was too quickly warmed by the filming equipment. Going down to 0 F worked, but according to Roizman Friedkin decided on the maximum in order to improve the actors' performance. "An actor on his knees for 15 minutes at 20 below zero is really going to feel cold. It worked out very well."

Once the actors' breath appeared, it was necessary to backlight the actors, which while it is easy enough to do in still photography is much harder when filming a movie. "[W]ith the actors moving all the time, it got to be a bit difficult. It was always a matter of finding a place to hide the backlight and finding a way to keep it off of the actors", Roizman said.

Blair wore green contact lenses meant to give her eyes a bestial appearance for scenes when Regan is possessed. To accentuate them, the crew used a soft light with its barn doors nearly closed to throw a narrow strip of light across her eyes. "It's probably a 75 mm lens, because we used that a lot", Friedkin recalls.

It was easier to film some of the other supernatural manifestations, such as the bed rocking and the curtains blowing, in Regan's room, since the walls and ceiling of the set were wild, or capable of being moved to accommodate a camera; after the scene where the ceiling cracks it was necessary to use a hard one. A hole was cut in the ceiling for the rig to go through when Regan levitates as the priests chant "The power of Christ compels you!", the most challenging shot in the sequence. the 80 lb Blair wore a bodysuit under her nightgown with attached hooks for monofilament wires.

Roizman said that while he had filmed similar scenes in television commercials, painting the wires to match the background so they would not show on camera was difficult on The Exorcist because of the changes in background. "We had to practically paint them frame by frame", he told the magazine. While most directors would have been satisfied with smoothing out the scene in postproduction, Friedkin wanted it in longer takes. Roizman's painting was so effective that it was unnecessary to apply any digital editing to that scene to prepare it for optical media release in the late 2000s.

Friedkin decided that he did not want any scenes in the movie to have "any kind of spooky lights that you typically saw in horror films", so all the lights in the bedroom come from a visible source. This was challenging because at one point one of the lamps falls on the floor, changing the way it had to be lit to preserve the impression of available light. At other times they flicker and dim, supposedly due to Pazuzu's influence. Lastly, at the end of the sequence, Friedkin wanted the lighting's mood to change, to "have an ethereal quality—a very soft, glowing, cool sort of thing" without any apparent change in its sources. "We tried, at that point, to work with absolutely no shadows in the room, using just bounce light—and I think we achieved the correct overall effect."

Since it was so necessary to hide the lights with such a small room and so many people in it both on and off camera, Roizman and his crew mostly used "inkies", small incandescent bulb lights usually used to accentuate objects within the frame, "hidden wherever we could find a place for one. We were constantly controlling them with dimmers, so that if someone got too close to one, we'd take it down." He recalls his gaffer at one point controlling four of them; as a joke he put sheet music in front of the man one day. Due to the low light used, it was necessary to use wide aperture settings in most of the interiors, not just Regan's room. "I shot 90 percent of the picture wide open, as usual."

The room's color scheme also worked to create the impression of black and white. The walls were a gray taupe, Regan's bedding a neutral beige, and the priests wore black. White, according to Roizman, would have been too dominant. "In toning everything down like this, the only real color in the room became the skin tones—an effect which I personally like very much", he said. "This sequence has an almost black and white feeling; yet, there is subtle color there."

Father Merrin's arrival scene
Father Merrin's arrival scene was filmed on Max von Sydow's first day on set. The scene where he steps out of a cab and stands in front of the MacNeil residence, silhouetted in a misty streetlamp's glow and staring up at a beam of light from a bedroom window, is one of the most famous scenes in the movie, used for film posters and home media release covers. It was inspired by René Magritte's 1954 painting Empire of Light (L'Empire des lumières).

Friedkin wanted to evoke visually the language Blatty used in the novel for this scene, likening Merrin to "a melancholy traveler frozen in time", standing next to a streetlight in the fog when he gets out of the cab. He gave the crew a full day to light the scene, using mainly arc lights and tripod-mounted "troopers", and boosting the brightness of the existing streetlamps. "After a great deal of trial and error, we filmed on the second night."

Roizman said of all the nighttime exterior shots in the film, Merrin's arrival was "the trickiest". In order to get the beam of light the way Friedkin wanted it, the crew had to take the window frame out of the facade they had attached to the house for filming, put it behind the window and then put the spotlight in between the window and frame. "[I]t was difficult to get that bright of a glow from a shaded window and we also had to hold a fog effect all the way down the street", Roizman said. "Of course—wouldn't you know—just as we were ready to shoot, the wind came up, which made it more difficult to keep the fog settled in." By working quickly, he and the camera crew were able to get the shot, which satisfied Friedkin on the first take. At the time Roizman recounted this, the film had not yet been released and, based on dailies he had seen during production (which he allowed were not shown under the best possible conditions), he might have overlit the scene out of fear of missing detail. "However, with proper printing, I'm sure it will come out dark enough."

Head spinning
The scenes where the possessed Regan's head rotates 180 degrees so that she appears to be looking directly backwards drew significant notice from audiences and critics when the film was released. "All I can tell you is that the way you think I did it is not the way we did it," Friedkin told Castle of Frankenstein at the time. Like other special effects in the film, it was performed live in front of the camera. A life-size animated dummy of the character was built, one so realistic that Blair felt uncomfortable in its presence.

Critic Mark Kermode says the scene's impact results from the audience not having expected it so soon after the crucifix scene. He believes its recurrence later in the film, during the exorcism scenes, was added on set since it is in neither the novel nor the screenplay. Blatty had argued against it, telling Friedkin "supernatural doesn't mean impossible", which led Friedkin to insert a shot of Karras, suggesting the scene might just be a hallucination. When audiences reacted strongly to it, Blatty said Friedkin had "prov[ed] me an idiot once again."

Special effects supervisor Marcel Vercoutere built the dummy, primarily of latex based on casts of Blair's body, with help from makeup artist Dick Smith. They tested its realism by putting it in the front seat of a New York City taxicab and, when enough people were looking, turning the head. They had given the dummy's face the capability to move and appear to speak, even adding a condom so its throat would bulge when speaking, but it still did not quite look real in the bedroom set. Then Roizman noted that unlike the other characters in the scene, it did not exhale, so its breath was not visible in the chilled air, and a tube was added for simulated breathing, which produced the requisite clouds of vapor.

Crucifix scene
The scene where the possessed Regan masturbates with a crucifix was filmed with Dietz playing the character since Blair was too young. To make it seem bloody, she struck it against a sponge soaked in stage blood that had been taped to her stomach. Dietz and Friedkin had a lengthy discussion before filming it about exactly how she was to move her arm. "[H]is method wasn't correct, well, anatomically speaking", she recalls. "We had this long discussion about the right way to jerk off and I showed him why a woman has to churn her wrist [more than a man does]."

As they were arguing about this, a photographer visiting the set was taking pictures of the two of them. When Friedkin saw this, he went over to the photographer, removed their film from the camera, and tore it up, then cleared the set so the two could consider the sensitive discussion privately. Dietz was appreciative of this display of control on his part. "He knew how to create an environment where horror actors would be at their best."

"This particular scene is the most thought about and talked about scene for the obvious reason that it programs two things that are generally not programmed up-front in the human mind ... sex and religion", Friedkin said at the time. It lasts only 50 seconds, yet to many viewers seems much longer, he noted. He had filmed much more, but ultimately decided, on his own without previewing it or consulting anyone, that it was about "how much I could take". While other directors might have used more (he joked that Russ Meyer might have made it the entire movie), "to me, it was worth about 50 seconds."

"Far from shying away from the sight, Friedkin puts it centre-screen, overlighting the entire sequence and accompanying the visuals with a truly revolting stabbing sound," writes Kermode. He quotes Blatty, who recalls Friedkin telling him that people would come to the film to see the crucifix scene more than any other. "At the time ... I thought he was destroying the film. But when I perceived that he was absolutely right, I thought it was terribly depressing."

Angiography scene
The angiography scene, in which a needle is inserted into Regan's neck and spurts blood, as Blair undergoes the steps of the actual procedure, caused audiences the most discomfort, according to Blatty, who himself admitted he never watched it when viewing the film. "I've learned over the years that [it's] the most terrifying scene", Friedkin said in 2015. "Medical science impinging upon the innocence of this little girl. Which is more disturbing than the demon."

Roizman recalled the challenges of filming the scene in his American Cinematographer interview. It was shot with limited time available on a Saturday afternoon, in one of the actual rooms used for the procedure. "The space was cramped and there was really no room for rigging lighting equipment, so I decided to shoot the whole thing with available light, which, in this case, meant fluorescent light." Unlike most of the other interiors in the film, that was more than enough light to be adequate and he was able to use a narrower aperture. Roizman's crew changed the light bulbs in the hallways so they would be the same color as those in the examining room. He was so pleased with the resulting footage that, for a later scene shot at a medical complex on Long Island, where they had more space and control, they again used the existing fluorescent lighting with just some color correction filters in the camera and exterior light from the shades to compensate. "[T]here was virtually no correction necessary in the lab, and the results were the best that I've ever had with fluorescents."

Reception
It has been criticized as "unappetizing", the film's "most needless scene", and "revolting". British comedian Graeme Garden, who has a medical degree, agreed the scene was "genuinely disturbing" in his review for the New Scientist; he called it "the really irresponsible feature of this film".

"The camera pointedly does not express the horror of Regan's experience with modern medicine, it only records it, allowing the audience to take away from it what it will", writes critic John Kenneth Muir of this scene in Horror Films of the 1970s. "In some ways, the hospital interlude is the most terrifying scene in the film because it looks, sounds and feels totally real ... For a time, it is medicine that possesses Regan, not the Devil, it seems." Kermode says it "seems like an Inquisitional torture, perverse in its precision and horribly sexual in its execution."

In a 2021 article in the journal History of the Human Sciences, Amy C. Chambers of Manchester Metropolitan University similarly observes that "[t]he medical space is made spectacular and horrific in The Exorcist not through the presentation of Regan's behaviour or the demon, but through the clinical nature of her treatment and how this is communicated through shots and sound." She quotes Finnish media professor Frans Ilkka Mäyrä on how the scientific suggests the spiritual here: "The violent movements and noises of arteriographic machinery reach diabolical dimensions. The names of medication gain occult resonances: Ritalin, Librium."

For another commentator, the scene heightens the conflict between religion and science at the time. "Not only were popular religious beliefs brought into question," Pamela Morrow wrote 40 years after The Exorcist's release, "but there was also the emergence of medical practices and disorders that were not yet fully understood ... By wrongly diagnosing Regan with a relatively new disorder at the time (Attention Deficit Disorder) and prescribing Ritalin, it exaggerates an implicit question. If there really is no God, and technology is unable to create cures and provide answers, then what will happen in the future?"

Medical professionals have described the scene, not in the novel but added to the film to reflect changes in medical technology, as a realistic depiction of the procedure. It is also of historical interest in the field, as around the time of the film's release, radiologists had begun to stop using the carotid artery for the puncture (as they do in the film) in favor of a more distant artery. It has also been described as the most realistic depiction of a medical procedure in a popular film. In his 2012 commentary on the DVD release of the 2000 cut, Friedkin claimed that the scene was used as a training film for radiologists for years after the film's release.

"Spider-walk" scene
Stuntwoman Ann Miles performed the spider-walk scene in November 1972, after having practiced it for two weeks. Vercoutere had designed a special harness, but she did not need it—as a former college gymnast at Florida State she was already a skilled enough contortionist Friedkin cut it over Blatty's objection just prior to the premiere, since he thought it appeared too early in the film for such a drastic effect on Regan to be visible. Whether the scene had been shot at all was debated by fans for years afterwards—Friedkin denied having done so—until Kermode found the footage in Warners' archives while researching his book on the film in the mid-1990s. When he showed it to Friedkin, the director said he had probably forgotten filming the scene. It was restored to the 2000 director's cut, albeit with a "muddy, grainy" look that one critic said made the scene seem superfluous, using a different take showing Regan with blood flowing from her mouth.

Miles was not credited. Websites devoted to the film during the early 21st century gave credit to another contortionist, Sylvia Hager, who had been credited after the 2000 re-release. This confusion may have arisen from Vercourtere's website, where he credited her and described the harness he had designed that she supposedly wore to make the scene possible. He blamed the inability to erase it from the film for its exclusion. Miles has recalled that in reality Hager, her lighting double, was unable to perform the scene even with the harness, which Vercourtere had hoped to bring to market afterwards. Since she was able to do the spider walk without it, she believes he left her out of his account for commercial reasons. The misidentification, Miles said in 2018, cost her jobs afterwards since some producers believed she was falsely taking credit for Hager's work. Since then, due to the intercession of the SAG, she has been properly credited.

Special effects
The Exorcist has several special effects, engineered by makeup artist Smith. In one scene, Max von Sydow is actually wearing more makeup than Linda Blair, as Friedkin wanted some very detailed facial close-ups. The 44-year-old von Sydow was made up to look 30 years older. Many viewers did not realize he was made up at all, which Alan McKenzie calls "a tribute" to Smith; critic Pauline Kael, whose review of the film in The New Yorker was generally unfavorable, called it "one of the most convincing aging jobs I've ever seen" According to Friedkin, it took four hours to apply the makeup every morning. "Dick Smith just happens to be the best in the world", he says. He said that if there was a regular Academy Award for makeup, Smith would have received it.

For the look of the possessed Regan, Friedkin and Smith drew their inspiration from the crucifix scene. If she had injured herself masturbating with it, they reasoned, it was likely that under Pazuzu's control she might also have deliberately scourged her face. "[So we] decided to have the makeup grow out of self-inflicted wounds to the face that become gangrenous so that there was an organic reason for the change in her facial features, which might certainly be demonic possession, or self-immolation", Friedkin later explained.

A latex stomach was built for the scene where the words "HELP ME" appear to be written on the possessed Regan's body. The letters were scratched in, and then heated to make them disappear. This part of the process was filmed and then run backward in the edit so the letters seemed to be appearing in the finished film.

It took Vercoutere some time to develop a convincing way to make Regan's bed shake. He eventually built three different versions of the bed to do different things. The set itself was mounted on eight pneumatic wheels so it could rock and quake.

Editing
After production finally wrapped, editing began in a suite at 666 Fifth Avenue in Manhattan. Bud Smith, who had gotten to know Friedkin while he was working on Putney Swope and other films with Robert Downey Sr. during the production of The French Connection, recalls Friedkin calling and asking him to work on The Exorcist after shooting was done. Friedkin had already hired three other editors (Jordan Leonduopoulos, credited as "supervising editor", Norman Gay and Evan Lottman), but told Smith he would be the lead editor. Seeing how much film there was to edit, he asked Friedkin if he could take one large rack of footage and try cutting it. It was the Iraq sequence at the beginning of the film, and after Friedkin disliked his first attempt, Smith worked through a weekend to recut the footage to a rhythm based on the sound of a blacksmith hammering an anvil near where Father Merrin is having his tea, a change that the director liked more. Early on, he cut many of the exposition scenes early in the film, such as Regan and Chris's trip around Washington to see the monuments and other tourist attractions, feeling that "they didn't really pertain to where this film was going."

While working on the film, Smith also created a trailer for the film known as the "flash face" trailer. After starting with Merrin's arrival scene and a voiceover broadly explaining what is happening, it cuts to a montage of faces from various scenes in the film, still, all appearing in all-white against a black background, which quickly swells to almost all white and then fades back to nearly black, making a strobe-like effect, as tense string music plays, ending after almost a minute and a half with the title. Friedkin said in 2018 that Warners declined to use it as they feared it would scare audiences too much. He considers it the best trailer made for the film.

In his tweet discussing this, Friedkin referred to Smith as "the film's editor", although the other three were credited. During principal photography, the editor then hired had never worked on a movie before and was forbidden from making any cuts to the raw footage. After shooting wrapped, he hired Lottman and closely supervised his work as he began editing. "It was all about power," Lottman said. "He wanted to be in control of the film." All four shared the Academy Award nomination the film received for its editing.

Studio executives suggested transposing two scenes early in the film: Karras's confession to Father Tom in the bar that he believes he has lost his faith and his visit to his mother. Originally they came in that order, as in the script; by reversing them, critic Mark Kermode says, the film shows Karras's mother's predicament as a direct cause of his spiritual crisis. This created a slight continuity error: in the scene following the bar confession, Chris goes up to the attic looking into the noises Regan has reported there. It seems in the film to take place in the morning, but instead of wearing the morning dressing gown as she had earlier, she is wearing the same heavy brown robe she wore when talking to Regan the night before.

A later scene, with Regan's first doctor visit ending in her being prescribed Ritalin, was cut by Friedkin because he felt the audience would be expecting that Regan's difficulties were the result of her possession and an additional medical examination would delay the film: "One of the things I was conscious of doing while editing The Exorcist was and not stop in one place anywhere, where the audience could say 'Oh wait a minute fella'". Blatty responds that as a result of cutting this scene, another slight plot issue was created by the later scene where Chris tells Regan she will be fine as long as she takes her pills, as without the doctor visit this is the first time the pills are mentioned.

Friedkin's final cut was 140 minutes long; despite his insistence that it was perfect, Warners insisted he trim the film to much closer to two hours to allow for more showings each day. Blatty was willing to fight for the whole film as it was, but over his objections Friedkin cut roughly 10–12 minutes. Some of the excluded scenes were among Blatty's favorites, including the original ending, with Dyer and Kinderman connecting and agreeing to go to the movies together at some point, and a scene where Karras and Merrin take a break from the exorcism and discuss the demon's motivation for possessing Regan on the MacNeil stairs. These scenes had been in Blatty's novel, and he believed that in the movie they made it clearer at the end that good had triumphed and what was at stake.

Sound effects
Special sound effects for the film were created by Ron Nagle, Doc Siegel, Gonzalo Gavira, and Bob Fine. Nagle spent two weeks recording animal sounds, including bees, dogs, hamsters, and pigs; these were incorporated into the multilayered mix of the demon's voice. Gavira, whom Friedkin hired after hearing his work in El Topo, achieved the sound effect of Regan's head rotating by twisting a leather wallet.

Friedkin was personally involved in the sound mixing, which took four months. It was the last aspect of the film completed prior to release, finished only right before deadline. Jim Nelson, who Friedkin had hired to supervise the mixing, recalls the director being particularly demanding during this time, treating his then-girlfriend, who was among those assisting in the process, "like a dog". Nelson himself recalls going from "having a seven-year contract as his associate producer to the guy he hated most in the world—in two minutes" after Friedkin overheard him telling Calley on the phone that the sound editors were "basically finished". Friedkin also used the time to solicit opinions on sections of the film from anyone uninvolved, particularly one janitor in the building, and if he liked it, he decided that portion of the film was done.

Alleged subliminal imagery
Wilson Bryan Key wrote a whole chapter on the film in his book Media Sexploitation, alleging repeated use of subliminal and semi-subliminal imagery and sound effects. Key observed the use of the Pazuzu face (which Key assumed was Jason Miller in death mask makeup). He claimed that the safety padding on the bedposts was shaped to cast phallic shadows on the wall and that a skull face is superimposed into one of Father Merrin's breath clouds. Key identified the pig squeals in the sound mix and gave his opinion of the subliminal intent.

A detailed 1991 article in Video Watchdog examined the phenomenon, providing still frames with several uses of subliminal "flashing" throughout the film. Friedkin told the authors, "I saw subliminal cuts in a number of films before I ever put them in The Exorcist, and I thought it was a very effective storytelling device ... The subliminal editing in The Exorcist was done for dramatic effect — to create, achieve, and sustain a kind of dreamlike state." In an interview for a 1999 book about the film, Blatty addressed the controversy by explaining that, "There are no subliminal images. If you can see it, it's not subliminal."

Titles
The editing of the title sequence was the first major project for the film title designer Dan Perri. Friedkin had sought him out after seeing his work on Electra Glide in Blue, before The Exorcist was even completed. "It took a long time to design the simplicity of what we wound up using due to experimenting as the film changed shape". Perri recalled. "As [Friedkin] was tightening and evolving the story it would affect how the opening took place."

When Friedkin played for Perri the music he wanted to use over the opening titles, that pushed the title designer further in the direction of having the titles be very simple. "On screen, the fewer the elements, the more important each becomes. So we're dealing with two elements: a screen that's black and type, the name of the film." The only other elements besides the title that had to be at the beginning of the film were the studio's name, and Blatty's and Friedkin's. The latter two were not on the best of terms at the time, according to Perri (Blatty had sued Friedkin and the studio almost two months before the film's release to make sure his name was included in the opening credits ), which affected how he styled their names in the credits: "[Legally], their names had to be the same size but where Bill Blatty has three names, of course they had to be the same size." Perri first showed Friedkin a version in which both of them had their names in two-line stacks, but later changed it so Friedkin's name was on one line, to distinguish him slightly.

For the words themselves Perri chose to keep the Weiss Initials typeface that had been used on the cover of Blatty's novel. The filmmakers agreed the words had to be red, but it took time to agree on the exact shade. "When it's exposed against black it ... swells, it glows, it's very hard to control. I had to do a lot of exposure tests just to get the right red that wouldn't bloom."

Perri's input into the film's opening continued after those credits, as the music abruptly shifts to an ululating male voice and the scene to the archeological dig site in northern Iraq. Friedkin told him he wanted the film to begin with a sunrise, even though he had not filmed one while there on location. The closest shot he had was one filmed at midday, of the sun in an orange sky, with rising heat visible. "I suggested that we create an implied sunrise and that's what's in the film now", Perri says, "a very, very long fade in, like a 30-second fade in of the sun in the sky but in black and white. It very slowly dissolves into color" That image gave the film the sense of beginning it had lacked.

The title design was carried over into prerelease marketing for The Exorcist. Perri designed a poster with the scene where Merrin seems to be confronting the Pazuzu statute entirely in silhouette, an orange sky behind them and the film's title in orange below. It was used as an international teaser poster. "That went out in six languages and they gave me the translation in each language and I set the type in the same style and I fortunately was able to supervise the printing—silk screened rather than lithography—and printed thousands of each and they were distributed around the world", Perri recalls.

As a result of the success of The Exorcist, Perri went on to design opening titles for a number of major films including Taxi Driver (1976), Star Wars (1977), and Gangs of New York (2002). In a 2019 article where Perri discussed how he worked with Friedkin to create the credits, the Art of the Title website observed that the disjuncture between Georgetown and Iraq, "two locations with an unclear connection", the title sequence enhances the film by keeping the audience off balance until Merrin arrives at the MacNeils in the last act. "The film asks its audience to hold ideas, timelines, and locations on the other side of the world in mind", the site says. "The importance of these varied narratives of the main characters in the film allows The Exorcist to extend the battle between good and evil beyond a family home in Georgetown, Washington and reveal the demons that lurk all around us."

Music
Friedkin rejected Lalo Schifrin's working score. The composer had written six minutes of music for the initial trailer but audiences were reportedly too scared by its combination of sights and sounds. According to Schifrin, Warner executives told Friedkin to instruct him to tone it down with softer music, but he never did; Schifrin disclosed in 2005 that he believes this was in retaliation for an earlier "incident" between the two that he declined to describe as he was already going against legal advice by saying that much. Schifrin denies claims he used his original Exorcist music several years later for The Amityville Horror. According to a 1998 documentary, Friedkin fired Schifrin on the spot after he and a 110-member orchestra had finished recording the score, and threw the tapes away in the studio parking lot.

In his Castle of Frankenstein interview shortly after the film's release, Friedkin discussed the evolution of the film's music. He said he had hired a composer, whom he did not name, to write a score, "and he did a score all right, and I thought it was terrible, just overstated and dreadful." He decided instead to use the music he had given the composer as inspiration. "In other words, rather than get bad imitation Stravinsky, I might as well have the real thing." A later account holds that Schifrin's score, consisting of dissonant strings, percussion, and excerpts of Catholic liturgy such as Libera me and Tantum ergo sung by children, was too effective at evoking the audience's reactions, a task Friedkin wanted to leave to the images on screen. Polish avant-garde composer Krzysztof Penderecki's music, particularly Polymorphia by contrast, worked with the images to convey "a certain timbre to alienate the ordinary and natural scenes ... and charge them with negativity." He thus used Polymorphia early in the film with scenes of the MacNeils' apparently tranquil domestic life.

Bernard Herrmann, famous for his scores for Orson Welles and Alfred Hitchcock, including the staccato string bursts that accompanied the killings in Psycho, was offered the opportunity to score the finished film. He was flown from London to New York, where he viewed a rough cut, and declined. He felt the minimal opening credits deprived a composer of the opportunity to establish a musical mood with an overture, and only Welles' Citizen Kane had been able to overcome that. In a 1975 interview with High Fidelity magazine, Herrmann said that Friedkin objected to his intention to use an organ in the score, saying "I don't want any Catholic music in my picture" and insisted on sharing credit with him for the music.

In the liner notes for the soundtrack album of his 1977 film, Sorcerer, Friedkin wrote that if he had heard the music of Tangerine Dream earlier, then he would have had them score The Exorcist. Instead, he used modern classical compositions, including portions of the 1972 Cello Concerto No. 1, of Polymorphia, and other Penderecki pieces, Five Pieces for Orchestra by Austrian composer Anton Webern as well as some original music by Jack Nitzsche. Most of the music was heard only during scene transitions; Friedkin used very short excerpts of some of the pieces to forestall the possibility viewers would recognize them, detracting from the mood he wanted to create. The 2000 "Version You've Never Seen" features new music by Steve Boeddeker, as well as brief source music by Les Baxter. There are 17 minutes of music in a film slightly over two hours long. Friedkin was satisfied. "What I wanted", he said, "what I think we have in the film, is understated music. The music is just a presence like a cold hand on the back of your neck, rather than assertive."

What is now considered the movie's theme, the piano-based melody which opens Tubular Bells, the 1973 debut album by English progressive rock musician Mike Oldfield, became very popular after the film's release, although Oldfield was not impressed with the way it was used. Friedkin recalled in 2015 that he had wanted something like Brahms' "Lullaby" with "a kind of childhood feel". He had gone to see Calley, who did not understand what the director wanted, but directed him to the nearby music library, where he found Oldfield's record, which Warners was not planning to release. "But I listened to that refrain, and it hooked me, and we won the rights to it" he said. "I think it sold 10 or 20 million records. And it was an accident."

Besides "Tubular Bells", there is other previously recorded non-classical music in the film. The Allman Brothers' "Ramblin' Man" is playing in the background of the bar scene where Karras confesses his crisis of faith to Dyer. The Greek song playing on the radio when Karras leaves his mother's house is "Paramythaki mou" (My Tale), sung by Giannis Kalatzis. Lyricist Lefteris Papadopoulos said that a few years later, when he was in financial difficulties, he asked for some compensation. Part of Hans Werner Henze's 1966 composition Fantasia for Strings is played over the closing credits.

Production difficulties and purported curse
Principal photography began in August 1972; it was scheduled to last 105 days. Due to production problems and accidents on set, it took over 200 days to wrap. As a result, the film went $2.5 million ($ in ) over budget, ultimately costing the studio $12 million ($ in ).

Early on, the set for the interiors of the MacNeil house was destroyed by a fire started when a bird flew into a circuit breaker, with the exception of Regan's room, which remained unharmed. Rebuilding it delayed shooting for six weeks. Another set was severely damaged when the sprinkler system activated. A two-week delay resulted when the 10 ft statue of Pazuzu was shipped to Hong Kong instead of Iraq.

Injuries to cast and crew also affected production, with permanent consequences. Burstyn's back injury during the scene where the possessed Regan throws Chris backwards before the head-spinning, the take used in the film, left her unable to film for two weeks and using crutches for the remainder of the production; the coccyx fracture she suffered has caused her continuing problems since it was inadequately treated at the time. In 2018 she described it as "a permanent companion".

Blair also injured her back, fracturing her lower spine after being too loosely strapped to the bed when it was being rocked. That take was also used in the finished film. She developed scoliosis as a result: "[It] was far more serious than I ever imagined and really affected my health negatively for a long time." She further developed a lifelong aversion to cold due to having to spend so much time in the refrigerated bedroom set wearing only a nightgown and long underwear. A carpenter cut his thumb off and a lighting technician similarly lost a toe in another accident.

There were also more deaths among people connected with the film and their family members. Among the cast, MacGowran died a week after completing his scenes as Dennings with his character's death; Maliaros also passed away, like her character, before the film was finished. Deaths among or close to the crew included the night watchman and the operator of the refrigeration system for Regan's room, along with the assistant cameraman's newborn child.

Family members were also affected. Blair's grandfather died during the first week of production, and von Sydow had to return to Sweden after his first day on set shooting the entrance scene after he learned that his brother had died, adding another delay to the production. Miller's son Jordan, born with hydrocephalus, nearly died when, while he and his father were out at the beach, a motorcycle that unexpectedly appeared struck him, leaving him in critical condition and requiring weeks in intensive care.

Unfortunate events related to people and places in the movie continued after release. Several years later, Paul Bateson, the radiological technician in the angiography scene, was convicted of murder in the death of journalist Addison Verrill; in 2015 Hatra, the World Heritage Site where the prologue had been shot, was demolished by ISIL militants. Shortly after the 50th anniversary of the film's release, Jordan Miller died after being hit by a bus.

Friedkin believed that there might have been some supernatural interference with the film. "I'm not a convert to the occult", he told Castle of Frankenstein, "but after all I've seen on this film, I definitely believe in demonic possession ... We were plagued by strange and sinister things from the beginning." He said some striking visuals in the film had not been intended and could not be explained.

Vercourtere, the special effects supervisor, also felt uncomfortable working on the film. "There was definitely a feeling something [bad] could happen," he recalled. "I felt I was playing around with something I shouldn't be playing around with." Miller recounts receiving a medallion of the Virgin Mary from an old priest while reviewing his lines in a small restaurant in Georgetown's Jesuit quarters. The priest told him that according to Gnostic doctrine, the Devil retaliates against those who expose him for what he is, and that the medallion would protect him from that as long as he himself was careful. Concern among the production was significant enough that Friedkin asked Father Thomas Bermingham, the film's technical advisor (who also played Georgetown's president in the film), to perform an exorcism on the set. Bermingham instead blessed the cast and crew, believing that an actual exorcism would only make the cast more anxious.

British film historian Sarah Crowther alleges stories of the curse were in part disseminated by Warner's marketing department, which she believes was purposely courting controversy by releasing the film just after Christmas. "[They] spread speculation of the curse prior to release. It was an extremely hot topic in global media when it hit cinemas", she told inews.com in 2018, likening the curse to the elaborate marketing gimmicks employed by producer William Castle to stimulate viewer interest in his horror films during the 1960s.

Blair told Kermode in 1989 that stories of the supposed curse may have circulated because it helped viewers deal with the movie. "They chose to see a scary film, and maybe they wanted to believe all those rumors because it helped the whole process", she said. "Maybe they wanted to believe weird things happened because it helped them to be scared."

Crowther believes most of the aspects of the curse are really just the result of Friedkin's driving, relentless production over a prolonged period, which fatigued many members of the cast and crew. Blatty agreed, telling Kermode that Friedkin had started the "curse" story with an interview during production in which he blamed "devils" for the film's many delays. "But for God's sake", said Blatty, "if you shoot something for a year, people are going to get hurt, people are going to die ... these things just happen."

In 2000, Blatty joked that "There is no Exorcist curse. I am The Exorcist curse!" when asked if the death of Blair's pet mouse was possibly due to it.