Deliberate mistake: When Eddie and "Jennifer" are walking around the house alone, "Jennifer" is trying to tell Eddie that she's really Sara. But By the time she is explaining that her name is actually Sara and not "Jennifer", Eddie has disappeared. She doesn't find him until later... But from the moment she finds him (and he is talking to her) he calls her Sara... but he never actually heard her say that. He was gone. Also, after they all get back together, a few of the other people start calling her Sara as well....but no one actually heard her say that her name was Sara.
Continuity mistake: Right after Evelyn gets electroshocked, Blackburn takes off her mouth guard and a pool of blood leaks around her lips and down the side of her cheeks. In the next shot, there is a little bit on her lips, and a lot down the side of her cheeks, and several shots later she is seen with only a little dribble down her cheeks and none on her lips.