Revealing mistake: In the hut in the swamps Zack lights a candle. The resulting light is obviously from a spotlight because the flame and the shadows are perfectly still. (01:09:30)
Revealing mistake: When Sean Connery and the others are examining the corpse found in the water, the dead body's eyes blink. (01:01:05)
Revealing mistake: When Papet peers through a telescope, it's obvious that the lens cap is on.
Revealing mistake: When Danny DeVito brings home the 'bigger dog' he says for the new dog to go eat the little dog that always bothers him. He lets the dog go and the dog goes after the little one. But when they show the dog chasing the little one he almost runs right past him. There must have been a trainer on the other side of the set calling the dogs to come over because he wasn't chasing the little dog. (00:40:30)
Revealing mistake: When Arnold throws the bad guy through the glass door at the dress shop, it shatters a split second prior to him going through it. (00:55:40)
Revealing mistake: At the end of the movie, the main creature has the head of a human. However, in a number of shots you can see the actor's neck showing how they made the head "appear" to be attached to this creature.
Revealing mistake: The laser blasts the robots fire instantly exterminate or destroy most everything in their path. However, when the guys are shooting at them during the mall blast-out, the lasers suddenly don't do much damage at all.
Revealing mistake: As Sgt. Highway turns the dead body with a cigar in the pocket you can see its right arm move to avoid twisting. (01:38:05)
Revealing mistake: When Howard's running from the female bikers, Satan's Sluts, look closely at one and you can tell it's a guy in drag, one wearing a dark blond wig. (00:10:00)
Suggested correction: I was in this part of the movie, everyone in this scene (except for the duck) is female.
Revealing mistake: Binky and Turnip are waiting for Ted Danson to show up at the racetrack to place his bet. Turnip starts the first sequence peeping from holes carved into the magazine. As he begins walking, notice an old man with a grey jacket and a blue shirt, reading a newspaper, sitting, and immediately after he comes in frame, an elderly couple coming in from the left. The man is wearing a brown suit and shirt about the same colour. When there's the first cut (after the odd guy sticks the tongue out), the two are rushing towards the entrance, opposite way from before, and there's the blue shirted old man standing, and a moment later there's the brown shirt guy passing by, just fresh off walking in and with another person, not the woman from before. The same guy is also seen in the bathroom in the next scene. (00:18:20 - 00:20:10)
Revealing mistake: At the end when Katrina's skeleton flips off Keith, you can plainly see a crew member's hand moving the arm.
Revealing mistake: When Norman drives Dukes car into the pond, it's obvious no one is in it.
Revealing mistake: Von Ragnar's body is obviously a dummy as it falls off the dam and onto the rocks below.
Revealing mistake: When Lady Kong grabs Mitch before Kong rescues her - and when she later arrives at the dance - Mitch is replaced with a stiff dummy.
Revealing mistake: In the Director's Cut ending when Audrey II eats Seymour, it spits out his glasses, and they land in front of the camera. They pulled this off by having a pair of glasses inside the plant's mouth that would be yanked out by a string, and another pair of glasses would be dropped in front of the camera. However, the first pair gets caught in the teeth and fall back inside the mouth, but the other pair lands on the ground anyway.
Revealing mistake: When the bully's held up by Sam wires can be faintly seen.
Revealing mistake: Obvious stunt man for Carrie Snodgrass due to having brown hair while she's a dark blonde when hanging from an axe handle near the end of the movie. (01:35:09)
Revealing mistake: In the taxi scene Ferris' dad is reading a newspaper. On the front page is an article with the headline "Community rallies around sick youth." As the camera zooms in it's a fake headline to a real news article. The news article begins, "A Chicago policeman killed himself today after he... a Park Ridge office and... workers with a... revolver as he searched for his estranged wife who was hidden beneath a desk by a fellow worker".
Revealing mistake: The chairman parks his car in front of Bel Fuse Ltd. And goes upstairs. His car explodes, but does it in front of a different building, probably switching to a stage building front; the metal doors don't have vents anymore and there are visible join lines in the asphalt and the cement. (00:15:10 - 00:15:40)
Revealing mistake: The scene in the locker room when the bullies are dunking Marty in the toilet. Marty's "body" is a fake prop used - on the naked body mysteriously there is no penis or testicles. In addition to this, despite being turned completely upside down, Marty does not struggle in the slightest as he would in real life - he does not struggle at all exactly because it is a prop body being used.