Revealing mistake: The "rain" came straight down in evenly-spaced vertical lines; this was not "natural" rain. (00:27:22)
Revealing mistake: In one of the scenes in the ballroom you can see that the thumb claw of the head witch is put on top of her real thumb.
Revealing mistake: When Maya Rudolph and Tim Meadows are in their car at the drive-in theatre, whilst Maya Rudolph says "We got Hubie Dubois spying on everybody", there is a close-up shot of the wing mirror with Hubie's car reflected in it, along with several other cars and a building in the background also reflected. Despite being a reflection, any text or numbers reflected in the mirror are not reversed. The number plate on Hubie's car is spelled out forwards, and the sign "Salem Drive In" on the building in the background is spelled forwards also, and not reversed as they normally would be in a reflection. (00:49:17)
Revealing mistake: The green screened scene behind the ticket collector on the dock isn't moving. The waves on the water are paused, then the background is moving again in the next scene. (00:08:00)