Continuity mistake: Pay attention to the scene where Randy gets the call that the principal is dead and the rest of the group races off to try to see the body before they cut it down. Five or so people get up and run towards the door. When they are shown in the exterior shot running from the house to the car it is an entirely different group that are not even dressed similarly. This was due to the fact that the group were made up of actors whose contracts were by the week. The exterior shot was the only thing they didn't get during that initial week and to bring them back for that one shot they would have had to have been paid for an entire new week, which was too expensive for one shot. They just used extras instead.
Continuity mistake: At the very end, when Sid finds out who the killers are, they are all standing in the kitchen. When Billy and Stu stab each other take a look at the blood stain on the left side of Stu's jumper. It starts around his shoulder and vertically goes down towards his waist. When Sid is fighting him in the lounge she gets up and goes behind the TV. In the shot looking straight down on Stu from a birds eye view, notice the blood stain is now horizontally across his stomach. You'll have to look closely for this one.
Continuity mistake: When Casey is making popcorn, firstly the top of the popcorn that she tears off and places next to the stove changes from being folded in half, to later on laying down flat. Secondly Casey picks up a salt shaker and places it by the stove, but this later disappears. (00:01:25 - 00:03:30)Hamster
Continuity mistake: At the beginning of the film, Casey is cooking popcorn on the stove. When she peels the top off, you see her peel the side away from the handle, and she's using her left hand, but when the shot changes, she's using her right hand, and is pulling from the other side. (00:01:15)Hamster
Continuity mistake: The Halloween scenes in the movie don't match up. For example, Randy is watching the part where JLC first discovers the bodies. About ten movie minutes later in Halloween, she's hiding from Michael Myers in the closet. Then Billy gets the idea to search for Sidney, because that's the scene currently playing. Too much time occurs between scenes for this to occur.
Continuity mistake: When the killer sneaks up on Randy, Randy is lying back against the sofa. When Ghostface raises the knife Randy is lying back, relaxed with a tired look on his face. On the delayed footage when the killer raises the knife, Randy leans forward and is practically on the edge of the seat, his mouth and eyes wide open.