Revealing mistake: When Loomis shoots the marshal's window out, when he makes a u-turn you can see the tire marks on the road and dirt from previous takes.
Revealing mistake: At the end of the film when Ginny and Paul are fighting Jason, his machete hits the shrine where his mother's head is displayed and where Terri's body is strewn. When the machete hits, Terri flinches, even though she is dead. (01:16:00)
Revealing mistake: When Ash shoots Cheryl through the door in the head, you can clearly see the hose (not an artery) that's squirting out the blood. (01:16:14)
Revealing mistake: When the father moves to close his dead daughter's eyes, the daughter's eyes close before the fathers fingers close them.
Revealing mistake: When the skull the children leave at the caretaker's hut falls over and engulfs him in flames you can see the stuntman's protective head gear.
Revealing mistake: When Joe has died of blood poisoning there is a close up of his head and neck, you can see him breathing and his eyes flicker.
Revealing mistake: When the two station reporters are investigating Eddie's room, as the female bends down to the table, she is scared by a dog. In one shot you can see a black wire on the dog. (00:14:55)
Revealing mistake: During the fight between Harry and TG near the end, several times you can see when TG hits Harry that the spade bends. (01:21:15)
Revealing mistake: The first time David werewolfizes, we're treated to the complete process... hair developing, bones painfully lengthening and twisting... and the torso of the actor very visibly halfway in the floor while all this is going on to the full-body werewolf prosthesis. Oh for computer graphics at the time to erase that detail of the process.
Revealing mistake: Obvious stunt doubles replace Cameron and Kim when they run from the telephone box just before it explodes. (01:20:09)
Revealing mistake: The Prowler's just killed Lisa in the pool, yet he's walking across a lawn completely dry. Clearly this is footage reused from when he was outside the dorm earlier.
Revealing mistake: During the flashback to Ginny's operation, you can tell it's a prop head due to the color of the part where the operation's taking place.
Revealing mistake: When John Jaffrey is lying dead in front of his medicine cabinet, he is still breathing.