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: A boulder tumbles towards James Mason and his party though a cave. With all the smashing against the walls and floor of the cave, the boulder stays entirely intact. However, just before the boulder hits a wall with two tunnels while flying through the air, the boulder now shows two majors fractures that were unseen earlier. The fractures were added to the boulder to give it a more dramatic impact by it breaking up with one piece nearly striking James Mason. (00:55:50)
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.