Continuity mistake: When the killer pops out from the closet after Sidney closed the front door, he's holding the knife above his head, but it cuts then to a shot of him raising the hand from a position below the waist. (00:28:35)
Continuity mistake: When Sidney manages to kick Ghostface away after he has almost stabbed her behind the front door of her house, she sets up the kick shouting "no" and shielding herself with her left arm, but in the shot of the actual kick the stuntwoman's left arm is on the ground. (00:28:55)
Continuity mistake: Billy holds Sidney in his arms after the attempt at her life downstairs. She clings to him and pulls at his jacket, that is unperturbed in the close-ups on Skeet Ulrich. (00:29:55)
Continuity mistake: At the police station, Billy looks back with anger at Sidney after the sheriff tells him that they have to detain him until the phone records come in. The sheriff is looking at him with his arms crossed, but in the close up on Skeet Ulrich the sheriff's got his hands on his thighs. (00:34:10)
Continuity mistake: When Tatum comforts Sidney telling her "I'm gonna get you out of here, okay?" in the background her brother comes out of the door holding the 'Father Death' costume box. The sheriff by him is holding an orange paper, but at the cut he's got his hand behind his back, no orange slip. (00:35:00)
Continuity mistake: The costume of Ghostface/Father Death is stuffed inside the plastic bag in two different ways in the shots when Sheriff Burke is checking it out - look at the bits coming out in the close-up. (00:35:05)
Continuity mistake: Tatum is growing impatient while Sidney is sitting in the police station waiting to be released, and she hurries her brother. In this sequence there is a blatant lack of continuity whenever the editing switches to reverse shots, as Rose McGowan's hand and Neve Campbell's movements don't match between angles. (00:35:25)
Continuity mistake: When Gale Weathers 'interviews' Sidney in the back alley, the microphone is turned at different angles between shots. (00:36:30)
Continuity mistake: When Sidney punches Gale in the face, she flies back against her cameraman that catches her putting his hand on her side under the armpit. In the next shot Kenny's hand is on the upper arm, and Gale is also already holding her cheek. (00:36:35)
Continuity mistake: Inside Tatum's bedroom, Dewey tosses Sidney an ice pack for her sore hand. Look at Rose McGowan's left hand; she's holding the plush bunny in a different spot between shots. (00:37:00)
Continuity mistake: Sidney is in Tatum's bedroom. Tatum is playing with her rabbit toy while Sidney turns the other way. Look at the notebook, pen, ice pack. Sidney doesn't do anything but a few seconds later Tatum's mom calls her and when Sidney turns towards her the objects have changed position. (00:37:10)
Continuity mistake: Sidney's right hand is in a different position in the two shots that happen when Tatum's mother tells her that there's someone at the phone for her. (00:37:30)
Continuity mistake: When Sidney tells Tatum to wait "Just a second" because she's going to talk to Gale outside school, Rose McGowan's bag has slipped off her shoulder during the take, but in the next shot she's wearing it properly. (00:39:55)
Continuity mistake: When Sidney walks towards Gale's van to talk to her the day after she socked her, she passes by the same two students in two shots. (00:40:00)
Continuity mistake: When Sidney is talking to Tatum and Stu by the lockers, the combination locks she's standing by are black in a closeup, but when a student runs past in a scream costume, she is by lockers with a pink and a turquoise colour lock. (00:40:50)
Continuity mistake: Gale realised that Cotton is innocent, and she talks about it to the cameraman. In that part of the scene, the sun is on Kenny at a different angle in different camera angles (look at the reflection of the rays in his hair and jacket). (00:41:55)
Continuity mistake: When some goof runs around the corridors of the school screaming, Neve Campbell's hair changes position over her shoulders between shots. (00:42:25)
Continuity mistake: Sidney bumps into Billy around the corner after she walked away from Tatum and Stu at the lockers. Behind Billy there's a short-haired student with a sleeveless striped top that turns the corner followed by a long-haired brunette. The two extras appear again in the next shot behind Sidney, taking almost 10 seconds to walk 2 meters. (00:43:00)
Continuity mistake: Mr. Himbry calls the two expelled students "Desensitized little sh*ts", pointing the open scissors at him. In the next shot he's looking at him but he changed position, since the scissors are gone from frame. (00:45:20)
Continuity mistake: When Sidney is in the bathroom at school, the trash on the floor around the trashcan changes. (00:45:25)
Answer: This is according to IMDb: When Sidney comes out of the closet and stabs Billy with an umbrella, the stunt man was supposed to hit a pad on Skeet Ulrich's chest. The first hit got the pad but the second one slipped and hit him in the chest (you can see it in his reaction). Wes Craven kept it in because of its authenticity.
Shannon Jackson