Revealing mistake: When the killer is attacking Cici on the balcony, you can see blood on Cici's back before she is even stabbed and both times she is stabbed, the knife that comes out of her back has no blood on it. (00:33:20)
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)

Continuity mistake: During the last stabbing of Maureen Evans, the killer puts his right arm around her and stabs her with his left; but from the back view, his left arm is around her, and he is stabbing her with his right. (00:10:20)
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)
Revealing mistake: Just before the cop gets impaled through the head by the pole, you can see that it is obviously a dummy. (01:23:45)

Continuity mistake: When Sidney wakes up and answers the phone, the position of the watch on the desk, beside the caller ID, changes between shots. (00:11:50)
Continuity mistake: When Cici is running away from the killer, when they reach the second floor of the sorority house the distance between them greatly increases between shots. (00:33:10)
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)

Continuity mistake: When Chief Hartley writes "Cici Cooper" on the chalkboard, between the closeup and wideshot of him writing, the handwriting and location of his writing dramatically changes, and the words "Maureen Evans" and "Phil Stevens" above, also change too. (00:41:20)
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: In the scene where Cici is killed, just before the killer throws her off the balcony there is a visible member of crew/stunt's head. (00:33:50)
Suggested correction: Very interesting! You have to watch the scene on Youtube or on an older DVD version because in BluRay I can attest the crewmember has been digitally erased and you can only see a tiny line where he was.

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)
Other mistake: In the beginning of the film above the box office the date says April 12. When Sidney looks at her watch the next morning it's not even close to that date. (00:00:35 - 00:12:55)
Suggested correction: The mistake is correct, but the watch part has nothing to do with the incorrect date. It is the next day.
Revealing mistake: When Mickey is flying through the air after getting shot at the end of the movie, if you look closely you can see it's a stunt double. (01:46:00)
Continuity mistake: When Gale kisses Dewey she has no more lipstick on her mouth, then in the next shot she has lipstick on.
Revealing mistake: When Mickey draws the gun at the end of the movie, a hammer is heard being pulled back. Yet the gun that Mickey is using is hammerless.
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)