Continuity mistake: At the start in the van, the girl you see smoking dope hands over her cigarette to the other kid. She uses her index finger and her thumb with the cigarette facing downwards, but in the next shot she has got it between her index finger and middle finger and it is facing upwards. (00:18:35)
Continuity mistake: When Shelly and Vera are walking out of the store, Vera stuffs Shelly's wallet into her beige pants. Later, while sitting on the dock, she pulls it out of her pink pants. She doesn't have a change of clothes with her. (00:31:05 - 00:56:40)
Continuity mistake: Jason has dark Khakis throughout the film, until the very end. When the cops are at the house, his body is in the barn wearing blue jeans. In part 4 he is still in blue jeans, but then changes into dark Khakis after leaving the hospital.