Visible crew/equipment: When Verbal drops the Zippo lighter in the police office, Chazz Palminteri leans down to pick it up. When he leans down out of frame, there are 2 "C-stands" visible in the background. These shiny, adjustable stands are general-purpose utility holders on a movie set, used to position lights and light control material for a setup (i.e. flags, scrims, diffusion, etc).
Other mistake: When Somerset goes back to the man's house alone, he cuts a sticker on the door with his switch-blade to get in. The first error is the sticker is on the inside and it says "Keep Out." The best part about it is the door opens inward. How did they put the sticker on the inside and then exit? (00:20:45)
Visible crew/equipment: When the Jeep is flipping, in one shot, the door flies open and reveals that Ace is wearing jeans. Ace doesn't wear jeans throughout the whole movie showing that this is a stunt double. When the car falls in the parking spot, Greenwall seen through the door is very obviously a dummy.
Visible crew/equipment: In the drive-in shootout scene, the camera and crew are visible in the rear view mirror in the cab of the white Dodge pickup fleeing De Niro and Kilmer.
Continuity mistake: When Dr. Elliot is doing his presentation, there is a large TV on a stand, with a VCR, which suddenly vanishes halfway through. (00:11:10)
Revealing mistake: When the plane first lands at Bangor airport, the words 'American Pride' on the plane are reversed, like they are reflected in a mirror in one shot as its wheels hits the runway. (00:50:55)
Continuity mistake: When Lucifer confronts Thomas, Lucifer forcefully pulls him closer and puts his right hand on his chest, but the close-up shows that his hand is under Thomas' arm. (01:21:20)