Continuity mistake: During the scene where Ness kills the Italian mobster in the lodge near the border, the moment he shoots him the wooden rail behind has two sticks underneath, half a second later, when the mobster is flying backwards dead, the sticks disappear, and a second afterwards, when he is laying dead, the rail's appearance has nothing to do with the previous two.
Continuity mistake: In the scene at the end when Arnie crawls into the booby trapped gully you can see the Predator behind him with the knives on his right arm already extended. The camera then switches to a shot of the Predator extending the knives to finish Arnie off. (01:37:34)
Continuity mistake: The car Carl Fox is driving is on a 3 lane road with concrete barriers, that does not allow for parking. When the camera angle changes to show the interior, the car is on a road with vehicles parked on the sides. (01:53:20)
Revealing mistake: When the baddie rises his hand to grab the frisbee with blades his hand is blatantly fake.
Other mistake: After Dan visits his wife in the hospital, he goes to Alex's apartment. In the scene where he's chasing Alex and crashes into the glass door, shattering it, look closely at his face and you'll see it's not Michael Douglas but a stunt double. A few seconds later when they are struggling in the kitchen, look again and you'll see the same stunt double.
Continuity mistake: When Jamie gets out of her car, her leg warmers reach down to her heels. In the next shot, they've been pulled up to just her ankles. (00:07:05)
Visible crew/equipment: When Angel walks on the sidewalk to the café to meet Louis Chyphre, there's a car passing close to the shot on whose window a crew member and the cameraman are reflected. (00:25:33)
Revealing mistake: When Paul Kersey blows up the restaurant, there are obvious dummies in the booth. (00:46:01)
Continuity mistake: When Molly Ringwald is on the phone at the club and gets approached by the girl in orange, throughout the whole conversation the position of the phone receiver in Randy's hand is wildly inconsistent. (00:09:30 - 00:11:00)