Continuity mistake: In the scene when Cindy comes out of the school where the jumper is on the roof, its very sunny just a few feet beyond the door. However in the shots where Cindy is facing the school and when she screams "What are you waiting for" - the area is now completely shaded.
Continuity mistake: During the "I Know What You Did Last Summer" sequence, after they swerve and hit the fisherman, their car is directly on the lines, but in the next shot it's not on the lines, then they are again.
Continuity mistake: When Cindy is walking away from the bum after giving him a sandwich, we see a white VW van driving away over her left shoulder. When the bum throws the sandwich back at her the van is parked back by the sign again.
Chosen answer: I know for sure they were making fun of the movie 'Usual Suspects' (dropping the cup) - they might have added the gag of the fish in it to appear as though she was shocked by the fish instead of the true identity of Doofy.