Revealing mistake: In many of the scenes taking place in outer space, if you look closely you can see polygon borders surrounding space vehicles (X-Wings, Star Destroyers, and even the Death Star) indicating the objects being superimposed into the outer space background. [This mistake may only apply to the Blu Ray version.]
Revealing mistake: When Superman gets blown away by the bombs, he is being smashed onto the rocks. You can easily see that the rocks aren't real, but also that when he rises up again, you can see the cardboard rocks dent.
Revealing mistake: When the cat rips the painting, it is already damaged before it touches it.
Revealing mistake: During the Amazon women sequence, when Niki gets pulled underwater you can tell by the movement of the water that it was shot in reverse. (00:49:32)
Revealing mistake: As Mr. Connor flies into the retaining wall after being thrown from the Vietnam setting, you can see the "stone" structure wobble.
Revealing mistake: When Denis runs out into the field after the nuclear attack, she brushes up against a dead cow, and the cow moves like a stuffed prop. Real cows are much heavier than that.
Revealing mistake: During the brawl in the 'saloon', the protagonist frees himself from the predicament that had him with a knife pointed at his throat. Cut to one of his friends who punches away one baddie, parries a strike and then "punches" someone else. Sarcastic quotes are needed here, because the straight punch misses its target. (00:44:35)