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. (01:22:55 - 01:23:30)
Continuity mistake: When Kenny the cameraman spots the front door open and turns around to look again at the truck, Sidney before the camera cuts away is turning all the way to look at the monitor as well, but in the next shot she's still facing Kenny. (01:23:35)
Continuity mistake: When the killer slits Kenny's throat, Sidney in the background stifles a shout with one hand on her mouth, both hands in the next shot. She opens her hands but her right hand is still glued to her face in a further cut. (01:23:40)
Continuity mistake: In the scene at the TV truck, the killer's knife is blood-free even after slicing the cameraman's throat and stabbing Sidney, if you look at him when he tries to open the door and when he gets in. When he shakes his fist at Sidney for running away though, the knife is all bloodied up. (01:24:00)
Continuity mistake: When Stu and Randy are begging Sidney at the front door accusing each other, Neve Campbell's hair is pressed against her body or on top of her right arm in different shots. (01:29:10)
Continuity mistake: Billy's expression is entirely different in the two shots when he raises his gun and points it at Randy. (01:30:25)
Continuity mistake: Look at Matthew Lillard once Billy says "What's the matter, Sidney? Looks like you've seen a ghost." He's scratching his cheek, but in the next shot his arm is down his side. (01:31:15)
Continuity mistake: When Billy is taunting Sidney saying the game is called "guess how am I gonna die" he is holding the voice box in a different way between shots. (01:31:20)
Continuity mistake: When Billy tells Sidney that her mother is the reason his parents split, he's pointing the knife at her, but not anymore in the reverse shot. (01:33:00)
Continuity mistake: Stu puts the voice box and the cellular phone inside the breast pocket of Sidney's father; the order is clear and visible even after Stu pushes the poor man to the ground; the white box is in front of the black phone. A minute later once they two-stooged their alibi we see again Mr. Prescott on the floor, and the two devices have swapped place in his pocket. (01:34:20 - 01:35:30)
Continuity mistake: It's stabbing time for the two idiot killers; Stu is about to plunge his knife into Billy. Notice Matthew Lillard's necklace as he says "I'll remember"; it's above the sweater. Cut (camera cut, that is), and it's under the sweater. Next time we see it, back to a previous angle and to the necklace being above the sweater. (01:35:10)
Continuity mistake: Once Billy is done slashing his accomplice, he points the knife at him and tells him what to do; the knife hand keeps changing position between shots. (01:36:00)
Continuity mistake: Finding out that the gun is gone, Stu whines "Houston, we've got a problem here." Sid in background turns towards him instantly, but she re-turns in the next shot. (01:36:35)
Continuity mistake: Gale falls back on the unconscious Dewey after Billy kicks her. Her jacket is draped across the chest touching the white button of her vest. When Billy gets on his knees by her though, the jacket is fully open. (01:37:30)
Continuity mistake: Stu is slumping against the desk and says he's dying. In the closer angles you can see his left fingers are coated in blood, but in wider angles (for instance when Billy grabs the receiver off him and yells "I'm gonna rip you up, you b**ch"), the fingers are cleaner. (01:38:40)
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 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: When Sidney bites Stu's hand, in close-up the wrist is well visible and displays the bracelet in full, but in the wider angle that section is entirely covered by the bloody sleeve. (01:40:35)
Continuity mistake: At the party at Stu's house, when Dep. Dewey is walking through the house looking for the killer, Dewey walks into the living room with the TV and couch. Look at the TV, there is a white phone sitting right next to it. Later, when Sydney and Stu are fighting and she is about to push the TV on top of him, the white phone is gone. The TV also appears to be bigger. (01:40:40)
Continuity mistake: In the close-up with Sid smashing the vase on Stu's head, her arm is bloodied all the way down to the elbow, while when she reached for the object the blood reached just about the wristwatch. (01:40:40)
