The scene where the demonic entity leaves Father Karras was originally done by filming Miller, Jason in possession makeup, then stopping the camera and shooting him again with the makeup removed.
This creates a noticeable jump in Father Karrass's position as he is unpossessed.
The 25th anniversary video releases smooths over the jumpy transition with a subtle computer morph effect.
Ellen Burstyn agreed to doing the movie only if her character didn't have to say the scripted line: "I believe in the devil!"
The producers agreed to eliminate the utterance.
Ellen Burstyn received a permanent spinal injury during filming.
In the sequence where she is thrown away from her possessed daughter, a harness jerked her hard away from the bed.
She fell on her coccyx and screamed in pain, which was filmed for the movie.
John Boorman had been offered the chance to direct "The Exorcist," but declined because he felt the storyline was "cruel towards children.
" He did, however, accept the offer to direct Exorcist II: The Heretic (1977).
Dana Plato was offered the role of Regan MacNeil.
Mercedes McCambridge had to sue Warner Brothers for credit as the voice of the demon.
There are semi-subliminal single-frame shots in this film: when the priest is dreaming of his mother coming up out of the subway, there is a single frame shot of a face (Eileen Dietz), painted black and white, grimacing.
There are two other places where this image is supposedly displayed: when Regan, lying on the bed, turns to look at Father Merrin and Father Karras, and just after the head-turning scene.
Jane Fonda and Shirley MacLaine were approached to play the role of Chris MacNeil.
Lalo Schifrin's score was rejected; see also Amityville Horror, The (1979).
CAMEO (William Peter Blatty): producer of the film that Chris is acting in; he's seen talking to Burke.
Directory William Friedkin went to some extraordinary lengths to abuse the cast.
He fired off guns behind the actors to get the required startled effect.
He was said to have slapped one actor across the face before rolling the camera.
He even went as far as to put Linda Blair and Ellen Burstyn in harnesses and have crew members yank them violently.
The bedroom set had to be refrigerated to capture the authentic icy breath of the actors in the exorcizing scenes.
Linda Blair, who was only in a flimsy nightgown, says to this day she cannot stand being cold.
There are tales about ominous events surrounding the year-long shoot, including the deaths of nine people associated with the production and stories about a mysterious fire that destroyed the set one weekend.
The agency representing Linda Blair overlooked her, recommending at least 30 other clients for the part of Regan.
Blair's mother brought her in herself to try out for the role.
Director Friedkin eventually asked technical advisor Rev.
Thomas Bermingham to exorcise the set.
He refused, saying an exorcism might increase anxiety.
Rev. Bermingham wound up visiting the set and gave a blessing and talk to reassure the cast and crew.