Revealing mistake: When Otto holds Archie upside-down, out the window, the rigid outline of the support is quite visible under Archie's pants' material. (00:59:55)
Revealing mistake: When they are observing the waxwork figures, it's obvious they are real people just trying to stand still, as you can easily notice the "wax" figures slightly rocking or moving, or the props they are holding doing the same.
Revealing mistake: When being chased by her uncle Elvira's hair moves in a way which indicates it's a wig.
Revealing mistake: After Joey and Ed leave the mausoleum, they discover the graveyard full of zombies. As one zombie staggers forward, near the front of the screen, he bumps a tomb and it wobbles. (00:27:25)
Revealing mistake: In the scene when the aliens first enter Valerie's house, Mac and Zeebo find the fish tank and eat one fish each. The shot turns to Valerie's stunned reaction then back to the aliens, who are smiling widely, pleased with their stunt. If you look at Mac's teeth, you can see they are bright white up to his first molar, which is a give-away at his fake white fronts.
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: After Johnny Five falls out the window and whips out his hang-glider, as he turns right-side up and soars past the buildings, you can see that his body is transparent (an artifact of the optical matting process used).
Revealing mistake: While Julius is talking to the man in front of the lingerie store on Hollywood Blvd, when the man's partner rides up on a motorcycle and tries to snatch the suitcase, we can see the stunt wire carabiner attached to the back of his jacket as he flies off. (00:12:30)
Revealing mistake: Near the end, when Eliot enters Frank's office with his rifle, he accidentally shoots into the ceiling. He shoots it at a slight angle, but the rubble falls right on top of his head instead.
Revealing mistake: In the scene where Zuckerman is thrown to the floor in the gym and handcuffed, you can hear the handcuff ratchet click as it's placed and closed on her wrist. As the other agent moves away, you can see that the handcuff is open and not actually closed around her wrist. (00:31:00 - 00:31:50)
Revealing mistake: When one character's killed, stomach sliced open, you can see the wire yanking open the prop stomach to the left of the camera.
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.