Revealing mistake: When Captain Needa is killed by Darth Vader because they lost track of the Millennium Falcon, in the background, two guards come to take him away. You can clearly see the dead captain get up almost by himself. (01:10:50)
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.
Revealing mistake: When Biro stabs the Imperial soldier with his sword, it's obvious that the sword is angled to miss his body. (01:30:50)
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.
Revealing mistake: When the Marines shoot the Japanese pilot, you can see the wire used to set off the blood bags coming out of his pants leg as he falls. (01:11:30)
Revealing mistake: When Caymans right hand man throws his spear through the bodies of two enemies, you can see that the part of the spear sticking out of the second guy isn't remotely in line with the spear going through the first guy.
Revealing mistake: After the press conference, there's a close-up of a newspaper ("The National Probe") which features obvious repetition of the same paragraphs over and over. (00:16:55)
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)