Continuity mistake: Shortly after the scene in which the killer pulls Randy into the van, Gale and Dewey run to the van and see the blood. Right before they open the door, there is a camera shot from inside the van through the window. You can see that the window is not broken: it is obvious that there is some sort of white fabric over it.
Revealing mistake: Towards the beginning, when Gale Weathers is talking to the sheriff who is standing at a podium, you see Mickey filming her with a hand-held camera. A panning shot going right following Mickey with some friends walking sideways reveals him looking at the camera twice. This is because he was waiting for his cue to stop.
Continuity mistake: In the beginning where Jada Pinkett Smith is stabbed in the back, you see a white girl to her right look down at her arm as Jada's blood lands on her. If you watch the background closely as Jad is dying and stumbling around, the same girl is still looking around, as if it just happened. (00:10:10)
Revealing mistake: At the start when Phil Stephens is being stabbed, when the killer draws back the knife you can see there is already blood on the knife. Its only there for a second so you have to look carefully. (00:07:45)