Revealing mistake: When the UFO makes the huge flash that knocks everyone in the cemetery down, one of the police officers kicks a tombstone as he falls and it wobbles back and forth. (00:13:35)
Revealing mistake: In the scene where the girl is going to shoot Vincent Price watch closely as she pulls the trigger. You can see the wires pulling the gun from beneath to give it the realism of the blast.
Revealing mistake: Near the beginning, when police Lieutenant Rowan is inquiring on the death of Ken Drake, there are only 4 men in the room, all facing one another in a wide shot. The camera cuts to a close-up of Dr. Bradford for a couple of seconds, and there is a distinct puff of cigarette smoke passing behind him, but none of the characters in this scene are smoking. Lieutenant Rowan does smoke later in the film (in fact, he's the only character who smokes), but he's not smoking in this early scene. Apparently, the close-up of Dr. Bradford was borrowed from omitted footage in which Lieutenant Rowan was smoking.
Revealing mistake: When Holmes kills the guineapig-human hybrid, the entire scene is ridiculous. In the first shot, the guineapig has tiny human hands that look to be about a half-inch at most. Holmes then steps on it, and in that shot it appears to be a different type of rodent entirely. Then we see the human hands under his shoe flexing in pain, and they look to be significantly bigger than before based on the scale of his shoe... at least 5X bigger than they were.