Continuity mistake: When Jack rips the door off the cab, he first breaks the top hinge and enters the cab. In the next shot when he pulls the cabbie out of the car, the door is completely off and laying on the ground. A few shots later when Jack grabs the newspaper, the door is seen hanging again. (01:40:10)
Continuity mistake: When they are in the ambulance, Danny screams 'I said, turn around!' and draws his gun. The next shot shows the driver looking to the rear and getting scared by the gun. In this shot you can see by the window that the car is totally stopped, and some car with a yellow light is passing by them. But in the very next shot, the ambulance is stopping (you can even hear the tires) and there is no car with the yellow light to be seen. (01:55:05)
Revealing mistake: There is an obvious shot splice of the elevator reaching the floor with Jack on it and one without him. The position of the elevator changes ever so slightly and you can tell the difference in the light coming from the elevator. (01:12:30)
Deliberate mistake: In the sequence where Jack finds his friend, and then the cards he is holding counts down to the explosion. Jack runs out, and the house explodes throwing the cop car into the air. If you look close, you can see the piston that launches the cop car and then falls back down. (00:24:40)
Deliberate mistake: Just before Danny enters the action movie, Jack Slater (Arnold) arrives at his 2nd cousin's house. Jack exits his car and jams his desert eagle pistol into his waistband. He then approaches the front door where he turns toward the camera to kick in the door. You can clearly see there is no gun in his waistband now. In the next shot he draws the gun from his waist. (00:22:50)
Visible crew/equipment: When Jack is in the real world, and he's playing chicken with the bad guy, as soon as Jack drives off on the ground, you can see a set of wires leading to Jack's car. (01:26:45)
Continuity mistake: Jack's shirt does not have bullet holes, as he walks up the stairs on the way to his apartment, but in the previous scene his shirt had bullet holes, as he packed up his stuff from his desk. (01:03:20)
Revealing mistake: When the chopper is about to shoot out the elevator, on the right is a pair of guns and on the left a gatling gun. At the end of the scene the guns have switched places, with the pair being on the left and the gatling gun on the right. Flipped shot. (01:16:10)
Continuity mistake: When Jack is speeding to get to the funeral at the hotel, he drives through the pond in front of the hotel. When the car goes in, it has the set of wheels it had throughout the film. When it emerges from the pond, it has a new set of white Cragers on it. (01:08:05)
Plot hole: It is firmly established in the last half of the film that movie characters and movie weapons do inflict damage and death in the real world. However, early in the film, a bundle of dynamite comes straight through the movie screen and explodes in the real world movie theatre. That quantity of dynamite should have gutted the theatre, easily; but, when Danny Madigan and Jack Slater cross from the movie world back into the real world, there is absolutely no damage to the theatre.
Other mistake: Before Jack's car jumps over the bridge, a van skids on the road. The first angle shows a thug firing at Jack, and the second angle shows Jack swerving to the left to dodge the bullets. The editing is all wrong here: The thug fires at the opposite lane to where Jack is, so he is really driving to where the bullets are.