The Night of the Tottering Tontine - S2-E16
Deliberate mistake: The knife that has just killed one of the investors doesn't have a trace of blood on it. No one had time to clean it off. (00:20:00)
The Wild Wild West (1965)
1 deliberate mistake in season 2
Starring: Robert Conrad, Dick Cangey, Ross Martin, Whitey Hughes
The Night of the Bubbling Death - S3-E1
Revealing mistake: As West drags the body of a bad guy out of the scene, the supposedly unconscious man is holding his head up so as not to have his head dragged through the dirt. A truly unconscious person's head would flop back on to the ground.
Trivia: Due to the rigorous stunts he performed, actor Robert Conrad would often rip out the seat of his already too tight pants.