Revealing mistake: It's clear that the sound of the ringing phone is impersonated by somebody vocally, off-screen.
Revealing mistake: When the gang tries the growth formula in the theatre, they quickly grow out of all their clothes until they are naked. But the scrunchy in Jean's pony tail is still in place and shows no signs of being stretched, even if the pony tail now is 20 times bigger.
Revealing mistake: Stan's car gets a flat from the severed Eye Creature's hand puncturing the tire. The scene shows the hand going for the tire and when it grabs it, the rubber fingers bend in and some bend sideways.
Revealing mistake: During practically every scene with Dr. Nadir, the prosthetics to make his cranium look more 'alien' are visible. In particular, when the Queen realises he's been shooting down spaceships and not missiles and calls him a 'fool', at the back of the neck the line where the concealing make-up ends is evident. Throughout the rest of the movie the other Martians have similar if not even more obvious bald caps. (00:17:45)