Revealing mistake: When Dolph goes into the bar near the beginning, he headbutts a bald guy. You can see that he doesn't even come close to making contact. Still, the guy has a broken nose.
Revealing mistake: In the bathroom scene when Debbie is attacked by the clowns from the medicine cabinet, you can see the holes where the puppets are being controlled from.
Revealing mistake: Clearly not Susan Blakely when she goes topless. Her hair suddenly becomes curlier, that's a body double.
Revealing mistake: When Jemma enters the headshrinker's laboratory, there is a table with three heads on it each encased in glass. When it goes in close-up on the middle head, you can see that the table has a hole where the actor can slip in his head.
Revealing mistake: When Bernard throws his gun to the ground, the ground "wiggles". (01:09:15)
Revealing mistake: Right before Dodger walks into Georgette's room in search of Oliver, she talks to herself in the mirror. But at one point the reflection moves when she doesn't. (00:43:10)
Revealing mistake: When Harry and Samantha are shot at in the elevator you can see a number of the dark marbles that were used for the effect rolling on the floor.