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: In Houston, when a man is thrown through a truck, notice the ground he falls on: The sand is leveled higher than the rest of the road around, obviously to hide a landing mat. Furthermore, after the fall the man turns around and he's got a bulgy square on the back to help for a safe stunt.
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: 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)
Revealing mistake: A policeman hilariously crashes his car because he was coming in too fast when the kids escaped the molegator. The car that explodes has square, all red emergency lights, but the car that was speeding through the street had red and blue lights of a different shape. (00:44:50)