Continuity mistake: In the scene with the crucifix, Chris falls to the floor after Regan bashes her in the face. Look closely at the dresser that eventually comes sliding across the room at her. When we first see it, it's about half a foot to the right of the closet door on the left of the room, and is never touched or moved. When we see it again as it comes sliding across the room at Chris it's been moved to the left right up against the closet door. (01:19:10)
Continuity mistake: Chris first meets Damien on a bridge as two other people walk in front of him. In the next shot they're behind him. (01:19:40)
Continuity mistake: Det. Kinderman talks to Chris as they're having coffee in the kitchen and says, "My opinion, he was killed by a very powerful man" and her right hand appears by her face between shots. (01:14:20)
Continuity mistake: As Father Karras talks to Det. Kinderman by the tennis court fence, the towel around his neck goes from being longer on the right side to longer on the left between shots. (01:05:40)
Continuity mistake: As they walk, Det. Kinderman talks about Burke Dennings death and Father Karras says, " Only what I read in the papers". Father Karras goes from not holding the towel around his neck to holding it between shots. (01:04:15)
Continuity mistake: The Psychiatrist hypnotizes Regan and the blanket on the chair behind her head is rearranged several times between shots. (01:01:50)
Continuity mistake: Chuck, the Assistant Director leaves after telling Chris and Sharon that Burke Dennings has been killed. In the next shot Chris' scarf is tied differently around the back of her neck. (01:00:30)
Continuity mistake: Chuck, the Assistant Director comes in and tells Chris and Sharon that Burke Dennings has been killed. Chris turns around and says, "Heard what" and in a bad over-dub we see her mouth move as she says something else that is been edited out. (00:59:50)
Continuity mistake: Chris drives home past the police cars and ambulance out side her house and when she gets in there's no one there. If you look closely as she turns into her driveway, tire marks on the wet pavement can be seen in the exact same spot from a previous take. (00:57:50)
Continuity mistake: After Burke Dennings is killed, Chris drives home past the police cars and ambulance out side her house with her high beams on. In the next shot as she pulls into her driveway, her low beams are on. (00:57:55)
Continuity mistake: Chris drives home past the police cars and ambulance outside her house after Burke Dennings is killed on the steps. At first there are a bunch of people on the steps, then the next time we see it two seconds later there's a lone policeman standing there. (00:57:45)
Continuity mistake: After he gets socked in the mouth, Dr. Klein gets ready to give Regan another injection and the lamp near the window and the curtain behind it move between shots. (00:54:00)
Continuity mistake: Dr. Klein gets socked in the mouth by Regan and blood drips out of his nose. The next time we see him, and in all the subsequent shots in this scene, there's no blood on his face. (00:53:40)
Continuity mistake: Dr. Klein talks to Chris about what Regan's test results indicate and she's touching her face with her left hand. In the next shot from the front, she's touching her face with her right hand. (00:48:05)
Continuity mistake: Dr. Klein and Dr. Taney arrive at the house and go up to Regan's room to see her for themselves. We see inside the room and the two doctors, Chris and Sharon are the only ones there but as they try to give her an injection, Karl appears from out of nowhere restraining her. (00:54:05)
Continuity mistake: As Father Karras lays down, Father Dyer shuts all the lights for him. The lamp on his desk is right over the typewriter the first time we see it than later as he turns it off it has been moved to the left. (00:46:10)
Continuity mistake: Father Dyer walks into Father Karras' room and the Chivas Regal bottle on the floor changes sides between shots. (00:45:10)
Continuity mistake: Father Dyer walks down the hall on his way to Father Karras' room and the florescent ceiling lamp closest to the window is turned off between shots. (00:44:55)
Continuity mistake: Regan screams, "Mother, make it stop" and the books near the lamp on her desk move to the right between shots. (00:44:40)
Continuity mistake: At the party Father Dyer sings just before Regan walks in and says to the Astronaut, "You're gonna die up there". The music book on the piano is open to the same page but the manuscript paper underneath has been moved between shots. (00:42:35)
Answer: The demon wants everyone to lose hope for the girl and give up on her. Her father, having already flown the coop, just makes this goal that much easier.
TonyPH