Audio problem: Near the end of the movie, when the Ambassador is dragging the child up the aisle of the church, in several spots you hear the child scream but his mouth isn't open. (01:45:35)
Audio problem: When the baboons are attacking the car, Damien screams, but his mouth doesn't open.
Audio problem: When Thorn and Jennings are at the apartment in Italy they are talking about Bugenhagen and Jennings says that he is an exorcist and has read about him. However, his lips continue to move even after he has finished speaking. Although the camera is on Thorn and Jennings is blurred in the background, his facial movements are still easy to see.
Chosen answer: The idea wasn't entirely Hollywood's. The antichrist is sometimes said to be "born of a jackal. " Jackals are mentioned in the Bible, and some interpretations consider them a symbol of something that is "not of God." In the movie, it means that the kid was scary as hell, literally.
Hobbes