Continuity mistake: When Ghostface is trying to kill Tatum in the garage, she tries to go through the doggie door. From the outside shot, she is out of the door from her arms and up. From the inside shot, she is out of the door from her hips and up. (01:04:20)
Continuity mistake: As Gale is talking to Dewey outside the school, when she is trying to get information from him about the killings, Dewey takes his sunglasses off and hangs them on his shirt. In the following scene they hang two different ways every time the camera cuts to him. (00:48:40)
Continuity mistake: After the curfew has taken effect, Dewey and Sheriff Burke are standing on a sidewalk in town. The Sheriff is smoking a cigarette. In one shot the cigarette is almost gone, then he drops it and he steps on it, but it's now a lot longer. (00:59:40)
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: When Tatum is throwing beer bottles at ghost face in the garage, there is beer and foam all over his costume...until he lands on the stairs behind her. (01:04:10)
Continuity mistake: After Sidney has been attacked and is in her room. Billy climbs through the open window. It is completely open. After he drops his mobile phone, the window is only half open. (00:28:35)
Continuity mistake: When Stu & Billy are in the kitchen after Sydney has escaped them, she calls Stu's house phone. Billy gets pissed and throws the receiver at Stu. It bounces off him and lands on the floor, yet when Stu picks up the receiver to talk to Sydney, it's on the table. (01:39:05)
Suggested correction: To be fair, Stu is shown having a grip on the phone's cord, and he had all the time to jerk it up on the desk overshooting his resting arm while he was off-camera during Billy's temper tantrum. Of course, it's also a known fact that Stu being hit and Matthew Lillard's reaction was an ad-lib kept in the final movie, so they were going to keep that take in the movie regardless - it might be a mistake, after all.
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: At the end of the movie when Stu and Sidney begin tumbling (right before he gets killed) there is a bench in the background with a bag of ruffle potato chips facing upwards, in the next shot it is lying down. (01:40:30)
Suggested correction: There are three bags of potato chips; rewatching the scene, does not seem to me any of them changes position or orientation except maybe the leftmost smallest one that turns flat on the back instead of showing the green strip. The change though happens as the camera is away for two cuts on Neve Campbell first, then on Matthew Lillard as they're struggling, which would reasonably affect the flimsy foil bag.
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 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)
Continuity mistake: When Dewey and Gale enter the house party Dewey jokingly takes a bottle of beer off a party goer then gives him it back. The bottle is back in Dewey's hand again when he speaks to Tatum. (01:03:40)
Continuity mistake: After Casey has been stabbed in the chest she falls down and the killer gets on top of her, before he can stab her again she knocks the knife out of his hand and the killer instead starts to strangle her. She then kicks him off her but you can see he still has the knife in one of his hands as he falls backwards. (00:11:00)
Continuity mistake: In the final scene where Sidney gives the "coup de grace" to Billy shooting him in the head after he suddenly woke up, he holds the left arm above the mask on his top left, but when he dies, his arm is lowered and the knife appears from nowhere. (01:42:30)
Continuity mistake: After the girl's dad leaves the room, Billy holds up a red stuffed bear against the bed. In this shot, the bear is only half sticking up at about its arm level, but in the next cut, it's high enough its feet are visible on the bed. Then only a second later as Billy starts to stand up, a jump cut has his arms go from down to outstretched with the bear instantly as he starts to stand. (00:14:10)
Continuity mistake: When Tatum calls Sidney at 7:15, she reaches over to get the phone. The sleeve is at her elbow in one camera angle, but it's instantly at her wrist in the shots before and after. (00:25:15)
Continuity mistake: When Sidney is in the bathroom at school, the trash on the floor around the trashcan changes. (00:45:25)
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)
Continuity mistake: When the killer and Sidney are fighting by the front door, the killer takes the knife and is ready to stab Sidney. Then Sidney kicks him, and he goes flying, then watch as it goes to a wide. He is now much higher in the air than he was a moment ago. (00:27:50)
Continuity mistake: When Sidney and Tatum arrive at Stu's party, they are dropped off by Dewey. Then the two girls walk to Stu's house. The bags Tatum is carrying are switched when they are walking inside the house (when she says "Catering is here"). (01:01:30)
