Continuity mistake: Rolland Tyler (the set-up special effects guru) and his F/X assistant Andy have one of the "dirty" cops in the truck of an old car. To get a confession out of him, they take him to a secluded place under a highway overpass and continue to ram the car, trunk first, into the overpass pillars with the cop still in the truck. The man buckles, but not before about six rear-end hits. Yet, there is very little dents or damage to the back of the car throughout the ordeal.
Plot hole: After Leo and the clerk finish looking up the fingerprints on the computer, the other cop says that the dead girl was dating Roland. When asked about Roland's address, the other cop says that he can probably find it somewhere and leaves the room. Leo is sitting directly in front of the computer that just gave them someone else's address.
Revealing mistake: After the girl is shot through the window and Tyler is beating on the sniper, he hits him with the gun. You can see the gun bend and shake, showing that it's rubber or another soft material. Even better when viewed in slow motion, it's very easy to see how much it bends.
Other mistake: After finding that he has run over a dummy and not a live person, the officer doesn't resume the car chase even though Roland's panel truck is shown driving only about one block ahead of him with no traffic in between. For those of you who don't know, panel trucks have the get-up-and-go of an arthritic turtle.