Continuity mistake: Near the beginning Buffy tears off her dress and throws it on the ground. When they walk away there's no sign of it. (00:09:20)
Continuity mistake: In the scene where Buffy and Cindy get dressed in the locker room, a girl standing right next to Buffy first drops her towel to get dressed and a few seconds later has the towel wrapped around again. (00:44:05)
Continuity mistake: In the scene where the killer is in Cindy's house, the killer is hiding behind the couch. When you see shots of the killer, the cell phone is in his right hand and the hook is in his left. When she notices him and he stands up, the phone is in his left hand and the hook is in his right. (00:33:30)
Continuity mistake: When the killer jumps up behind Ray and stabs him through the back with the hook, we see he obviously gets lots of blood on it. Watch it when he goes to stab Cindy and misses. It hits the cupboard and is completely clean. The hook is clean for the rest of the time he has it. (01:10:50)
Continuity mistake: At the end of the Matrix scene he throws Cindy into the wall, look when she hits the wall there is no sign of hitting the wall, but when she is falling to the ground they is an imprint like an oval on the wall. (01:11:05)
Continuity mistake: When the six characters are imitating the scene of I Know What You Did Last Summer, they get out of the car after it has spun around. All of the headlights are on, the two yellow and the two white. Later, if you look behind them, the left headlight is off. (00:15:45)
Continuity mistake: In the scene where Ray is killed, the killer stabs Ray with his hook. Ray's shirt is not bloody, but as he falls it is. Then when he lands on top of Bobby his shirt once more is clean. (01:10:50)
Continuity mistake: In the flashback of the gang killing the fisherman, Shortie drives up in his car and just as someone says, "Brenda take care of them" there is a shot of the car with no smoke inside it. The camera cuts to a view of Brenda approaching and the car is full of smoke. (00:17:30)
Continuity mistake: When the bottle is dropped in the car, it hits Cindy on the head and falls down in front of her. When Greg gets out he now has the bottle. (00:15:15)
Continuity mistake: When Greg stands up through the car's sun-roof, during the flashback, he is holding an empty bottle, but when he is at the top of the car the bottle is nearly full. (00:15:20)
Continuity mistake: In the scene after they look at Greg's report card, Ray has his hand on Brenda's ass, in the next angle it is on her shoulder. (00:12:05)
Continuity mistake: In the scene where they hit the fisherman, they spin the car. Notice the yellow line, they are somewhat over it in one scene, then in the next the line in to the right of the car, not under it. (00:15:55)
Continuity mistake: When the gang hit the guy with the car they all get out. When Greg gets out he only has the bottle in his hand but when the camera returns he is holding a flashlight. (00:16:00)
Continuity mistake: After the killer throws Cindy at the wall and then breaks the long table, Cindy runs and stands in front of the round side table and lamp, which are right beside the wicker chair. However, when she levitates, that table and lamp are now beside the couch.
Continuity mistake: When Buffy comes up to Greg and he is banging his fist up against the locker and cussing, you see his report card in on hand and you can see the outlining of the subjects but there is no "DUMB-ASS" stamp on it, but in the close-up there is.
Continuity mistake: When Bobby spews out, ahem, "the white stuff," it is all over the ceiling, but when it cuts back to Cindy and Bobby, it's not on the ceiling anymore.
Continuity mistake: When Drew goes to answer the door to the trick-or-treaters, the table to the left of the door has nothing on it. Yet when Drew sees the killer, a banana, grenade, knife and gun are now lined up on it. (00:02:15)
Continuity mistake: Near the end of the movie, when Ray is stabbing Bobby, Cindy says "You've watched one too many TV shows." Ray points the knife at her. At this point the knife is in his left hand but when he turns back round to stab Bobby again the knife is back in his right hand. There is not enough time for him to swap hands between shots. (01:10:25)
Continuity mistake: When Buffy is getting out of her Dad's car and starts to walk over to Brenda and Cindy, she steps over a curb in the street. When the shot faces Brenda and Cindy, instantly Buffy approaches them and has already crossed that big street. (00:09:15)
Continuity mistake: In the scene where there's a party at Cindy's house, two kids behind her are drinking liquor out of bottles that are completely upside-down, but the level of liquid remains constant. (00:57:00)
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.