There Were Giants in the Earth - S1-E5
Revealing mistake: The Robot's lights wink out for a few seconds as it disables the force field.
Revealing mistake: When Ultraman finally confronts the fake Ultraman (Zarab), one of the shots shows the two Ultramans rotating around, followed by a right-hand punch right to the fake's left neck. At the end of the shot, the suit actor can be seen wagging his right arm in mid-air, possibly hitting the neck too hard. What's even noticeable is that parts of the silver paint on the right glove fall off. (00:23:34)
Revealing mistake: At the very end before the credits, Cosby and Culp play stickball with kids on the street. Cosby races to reach a fire hydrant which he almost knocks over, revealing it to be a prop. (00:51:00)