The Werewolf - S1-E5
Revealing mistake: It is obviously a dummy in a woman's dress The Werewolf throws into the empty swimming pool.
Revealing mistake: When Major Popov aims the rocket launcher at the Venus probe, there is no rocket in the launcher- it is just an empty tube.
Backlash of the Hunter - S1-E1
Revealing mistake: The exterior shot of the house of the rich Miss Elias preceding Dr. Ruben Seelman's phone call, is a zoom on a static photography with a visible line on it. It is reused later in the episode (after Jim pulverizes his own picture in the phone book), with the exact same telling line. (00:30:20)