Revealing mistake: When Superman is looking down at the earth, the cloth the model is sitting on is evident in the bottom right corner. (00:22:40)
Adventures of Superman (1952)
1 revealing mistake in Panic in the Sky
Starring: George Reeves, Bill Kennedy, Jack Larson, John Hamilton
The Dog Who Knew Superman - S2-E9
Other mistake: A gangster pushes a dog into a well and the dog can be heard splashing around. The man's wife is furious and several people are unable to retrieve the dog. Superman tunnels into the ground and into the bottom of the well and emerges holding the dog. Both he and the dog are completely dry.
Lois Lane: Eureka.