Corrected entry: The movie establishes its own rules regarding the reality of the physical abuse suffered by the Regan character. Apparently, all the evil manifestations and physical damage suffered by Regan is real, for she has the scars at the end of the movie to show it. This shows that they are not just a mental trick played on the others by the 'demon'. So when Regan turns her head completely around at two different points in the movie, the actual physical damage she suffered should have killed her. You could even hear bones cracking during the sequence, suggesting that she was indeed going through some extreme physical suffering. Even if the 'demon' kept her body 'alive' with his special powers even though it should have been dead, Regan should have died moments after the 'demon' left her body and invaded Father Karras'.
Corrected entry: In the "Party Scene", Fr. Dyer tells Chris about the death of Fr. Karras's mother after Chris inquires about Fr. Karras. A few scenes later, when Fr. Karras first visits "Regan", she speaks to him about his mother. As he leaves the house he asks Chris if either she or Regan had knowledge of his mother's death and Chris says "No". Chris's answer to Fr. Karras helps the validity of the demonic theory, but doesn't match what took place previously in the movie (DVD).
Corrected entry: In the final scene, Regan's house has disappeared, in one shot, as the priest stands at the top of the stairs and looks at it.
Corrected entry: When Regan makes the room shake, the door and walls start cracking. Later in another scene the door is perfectly fine, with no crack in it.
Corrected entry: The bridge scene. Chris McNeil must have arranged to meet father Karras on the bridge. He walks up behind her, stops, and then says: "Mrs. McNeil?" She tells him to go away. He replies: "I should have told you I wouldn't be in uniform." There was no sign of her recognising him. But the film indicates that she must have seen him on several occasions and would have known who he was. Early on in the film she sees him talking to a younger priest and watches them for a few seconds. At the party she asks Father Dyer: "Who is the priest I keep seeing?" Father Dyer tells her that the priest is called Damian Karras and that he is a psychologist. Therefore she should have recognised him.
Corrected entry: When the priests are doing an exorcism on Reagan she floats above the bed and breaks the restraints that the doctors put on her from hurting anyone and herself. Then when she comes back down Father Karras rips a rope off the headboard and ties her hands together. Then she sits up and hits him in the back of the head. Later when Karras comes back in the room, as the other priest is in the bathroom, her hands are tied back to the bed in the restraints that she broke when she floated off the bed.