Revealing mistake: When Leslie is fighting the soldiers, one soldier hits a second soldier with his rifle. The rifle can be seen to bend around the soldier's body and then straighten again. (02:12:10)
Revealing mistake: After Manco beats up Cavanaugh and places Cavanaugh's back up against the bar, while Manco faces him, three of Cavanaugh's henchmen appear at the entrance of the bar demanding that Cavanaugh be released. Manco turns around and kills all of them with his pistol, while Cavanaugh falls to the floor crawling toward his gun. Manco is walking toward the entrance of the saloon with his back to Cavanaugh. Manco draws his gun and kills Cavanaugh without looking at him. If you look closely at the tip end of the pistol, you can see that the only thing that Manco would have killed was the saloon floor. (00:17:00)
Revealing mistake: It's clear that the sound of the ringing phone is impersonated by somebody vocally, off-screen.
Revealing mistake: In the opening sequence when Colonel Ryan's plane has crashed and is on fire, you can see a metal pole supporting a burning aircraft shell, not a real plane.
Revealing mistake: In the scene where a tank is being pushed to the side by another, it's clear the tanks are miniatures.
Revealing mistake: When the tail breaks off of the "German" machine and it careens around the field, you can see the little steerable tail wheel used to control the plane in those scenes. In all other scenes this plane has a tail skid.
Revealing mistake: Stan's car gets a flat from the severed Eye Creature's hand puncturing the tire. The scene shows the hand going for the tire and when it grabs it, the rubber fingers bend in and some bend sideways.
Revealing mistake: In the scene at the end of the movie where Lee Marvin is running interference during the escape by shooting in the air, horses pulling a beer wagon get startled and run into the street where the wagon turns over. At the beginning of the shot, when the horses begin to bolt, you can see the stuntman driving the wagon. He is sitting low behind the wooden front of the wagon (which has holes cut in it so he can see out).
Revealing mistake: At the very end, a violent storm engulfs Jerusalem and the people viewing the crucifixion. In the close ups, you can see rain falling, but no one appears to be getting wet.
Revealing mistake: In the scene where the boy is shot in the leg and the carried away by an unionist soldier you can see more union soldiers storm past them. The bayonets of the soldiers are obviously made of rubber as they are dangling while the rifles are moved up and down by the running soldiers.
Revealing mistake: During practically every scene with Dr. Nadir, the prosthetics to make his cranium look more 'alien' are visible. In particular, when the Queen realises he's been shooting down spaceships and not missiles and calls him a 'fool', at the back of the neck the line where the concealing make-up ends is evident. Throughout the rest of the movie the other Martians have similar if not even more obvious bald caps. (00:17:45)