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.
Continuity mistake: When Jack is being chased and the guys in the red pick up truck are throwing dynamite at him, they throw one that hits a parked car just as Jack makes a hard left turn. The next shot has the car exploding and Jack having made a hard right turn.
Revealing mistake: After Slater jumps out of the house and it explodes, when the cop car flips over, the air ram used to flip it over is visible.
Chosen answer: The kid points them out in the film, in order to convince Arnold's character that he inhabits movieland. Also, after Arnold's character falls into the tar pit he is able to completely wipe himself clean, an obvious intentional continuity error.