Revealing mistake: When Ripley first burns the egg plants inside the nest, the Queen screams and moves her head. The steel rod used to hold the Queen's head to the rest of her body is easily visible.
Revealing mistake: In the scene where Ronnie visits Brundlefly for the second time we see Brundlefly walking on the ceiling and wall, however his shirt doesn't remain consistent with gravity. This is especially obvious when he pulls his shirt up to show Ronnie his new tumor and then places it back down. The shirt appears to be being pulled up to towards the sky from Ronnie's perspective. (01:07:30)
Revealing mistake: When Number 5 is leading Number 3 into the toilet and moves at the last minute, you see Number 5 falling over, but in the next scene, he's perfectly fine.
Revealing mistake: The "blower" on the yellow Firebird never runs. NO wonder he couldn't beat the Wraith. (00:44:10)
Revealing mistake: After the bounty hunter, who changes three times throughout the movie, changes into the Reverend, he is in front of someone else who is a stand-in for the real Reverend but is obviously not.
Revealing mistake: When the ice-cream van is being shot at the end of the film, for a single shot you can see the driver sitting in it.
Revealing mistake: The initial fight with Fasil is supposed to take place in the parking garage underneath Madison Square Garden. But in the shot where wrestler Terry Gordy is smashing his head against the turnbuckle, a banner for the New Jersey Nets is visible in the upper left corner of the screen. The arena scenes were actually shot at the Meadowlands Arena in East Rutherford, New Jersey, where the Nets play.
Revealing mistake: Many times during the movie, when there is a close-up of the puckmarin, tiny wires can usually be seen attached to its arms.
Revealing mistake: When Chekhov falls on the aircraft carrier a cloud of dust flies up as if he's landed on a mat or soft cargo. When we see him on the floor it's concrete.
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: 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: When the bully's held up by Sam wires can be faintly seen.
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.