L'exorciste

When Regan projectile vomits at Father Karras, the vomit was intended to hit Jason Miller in the chest, but the plastic tubing misfired, hitting him in the face. His reaction of shock and disgust while wiping away the vomit is genuine, and Miller admitted in interviews that he was very angered by this mistake.

William Peter Blatty closely modeled the exorcism scene on the actual rite of exorcism in the Church's "Rituale Romanum". Father Merrin can be seen opening a copy of the Rituale in the scene in question. However, the priests depart from the Rituale in two important details. First, there should have been four people (apart from Regan) in the room during the exorcism: the exorcist himself; an assistant priest to take over in case the exorcist died midway through; a member of the victim's family of the same sex as the victim, to help restrain her; and a doctor, to (among other things) administer any medication that was needed. Due to the "2 Priest rule", Fr Merrin should have delayed the second round of the exorcism and phoned the bishop to get a replacement for Fr Karras, instead of trying to tackle it on his own.

There are no opening credits after the title. Although it is commonplace now, it was unheard of in 1973.

The network TV version originally broadcast on CBS in the '80s was edited by William Friedkin, who also shot a replacement insert of the Virgin Mary statue crying blood, replacing the shot of a more obscenely desecrated statue. Friedkin himself spoke the Demon's new, censored lines; he was unwilling to work with Mercedes McCambridge again. The lines "Your mother sucks cocks in hell, Karras" and "Shove it up your ass you faggot" were re-dubbed by Friedkin as "Your mother still rots in hell" and "Shut your face, you faggot." Several of Ellen Burstyn's lines were also re-dubbed by the actress, replacing "Jesus Christ" with "Judas Priest" and omitting the f-word. Most of the profanity spoken by Regan is also cut out, as are the shots of her being abused with a crucifix and forcing Chris' face into her crotch. There is also a slightly alternate shot of Regan's face morphed into the white face of the demon just after Merrin arrives at the MacNeil house (the theatrical versions only show the beginning of the transformation). This network TV version is rarely if ever used for TV and cable showings today.

Edited into Exorcist II: The Heretic: Alternate Opening (1977)