Audio problem: When Luke says, "Now all we gotta do is find this Yoda, if he even exists," if you look closely, his mouth never moves.
Factual error: Listening to a radio broadcast, live, since no other indication is given, Joe Louis is completing the 12th round of a fight. This is December 6, 1941. Joe's last fight of 1941 occurred in September, his next fight was January 1942. (00:00:10)
Revealing mistake: There are two times in the New York battle when you can see the actors are being filmed in front of a screen: 1. when Superman kicks Non, Superman in on film and Non is hovering in front of the screen. 2. When Ursa is flying towards Non and Superman with the flagpole, she is hovering in front of the screen.
Continuity mistake: The egg timer in the jail is about to run out, but when Dale runs over to it and tries to turn it over, there is more sand in it than before.
Revealing mistake: When Tony is having his first fight in the embassy, it is obvious that most of his punches do not connect at all. The people he supposedly hit still react as though being hit, and the sound effects of a fist hitting a jaw are still there, even if Tony misses by several inches.
Audio problem: When Benson is dismantling Hector and putting his brain in the container, he says 'What you can't stand, you run from,' but his lips don't match what he says. (00:48:50)
Other mistake: Near the end of the movie, Dave Speed jumps onto Torpedo's private plane and starts steering it to the ground. The plane is white with obvious red stripes. However, Dave Speed is supposed to lose his super powers when he sees red.
Audio problem: When the Kelvin sacrifice themselves in front of the Sonic Tank, Cowboy walks off and says, "C'mon, lets go", but his lips don't match what he says.
Visible crew/equipment: In the opening shot of the movie, several people (presumably the film crew) are reflected in the eye of the titular reptile. (00:00:15)
Revealing mistake: In this very-low-budget but star-studded flick about UFO contactees and cattle mutilations, Jan Michael Vincent's semi-auto handgun runs out of ammo during a firefight after firing only 3 rounds (the slide locks open, indicating the magazine is empty). Without reloading or racking the slide, Vincent continues firing 5 more rounds; but we see again, in close-up, that the slide is locked open, indicating an empty magazine. (01:00:55)