Visible crew/equipment: If you look really close in the background as the killer throws Cici off the balcony, you can see someone sitting in a tree, wearing black, with a camera. (00:33:35)
Continuity mistake: Hallie takes the remote control off the top of the TV to turn it on. But later when they return in front of the TV to watch the news report, the remote is back on the top of the set. Also, the position of the video console which is also on top of the TV has changed, the position of the clothing on the chair next to the television has repositioned and lastly, the items on the window sill behind the TV set have completely changed. (00:12:20 - 00:13:40)
Audio problem: When Dewey is being stabbed up against the soundproof glass, you see a shot of Gale shouting "No." You can see a reflection of the killer in the glass standing motionless, but you can hear Dewey being stabbed. (01:18:45)
Other mistake: When the killer is stabbing Randy, you can see his reflection in the side mirrors. He stabs him many times. The same amount of blood is on the knife every time he lifts it up. (01:02:45)
Revealing mistake: In the opening scene when Phil gets stabbed in the head, watch carefully and you can see the retractable blade popping back out when he pulls his head away. (00:08:05)
Visible crew/equipment: When Cici is killed, just before the killer throws her off the balcony there is a visible member of crew/stunt's head (this has been edited out in newer versions, but remains visible in others). (00:33:50)
Revealing mistake: When the killer attacks Sid's bodyguards, the younger one has blood on his throat before the killer slashes it.
Continuity mistake: When Sidney is about to get in the car with the policemen, she has a rather large noticeable spot on her chin. In the following scenes, it is gone.
Revealing mistake: When Cici is stabbed in the sorority house, her shirt is bloody, but there is not a hole in the material. (00:33:20)
Continuity mistake: When Gale kisses Dewey she has no more lipstick on her mouth, then in the next shot she has lipstick on.
Character mistake: During the scene in which they are all arguing whether or not film sequels are better than the original or not, someone says Sigourney Weaver's classic line from the movie Aliens: "Get away from her you bitch", and Randy makes a smart comeback and tries to correct him by saying "I think the correct line was 'stay away from her you bitch'. This is a film class, right?" Wrong - the first guy was right. This line is truly unconvincing for the Randy character, being a big movie buff and all. Jamie Kennedy decided to improvise as Joshua Jackson actually made the initial mistake by saying the wrong line, causing a different mistake. (00:16:25)