Revealing mistake: Throughout season 2 on several occasions it's clear that John Terry (Bob Warner) is wearing a fake mustache and a fake beard.
Revealing mistake: When Lazare shows up to talk to Will, we see that his left hand has been cut off. When Lazare is about to leave, he has his hands at his sides, and we can see that both arms are the same length, but the left one should be shorter, because it has no hand.
II (The Samurai called Jack) - S1-E2
Revealing mistake: When Jack cuts the flying car's hood off, he slashes it vertically, but it is cut horizontally.
Revealing mistake: At one point when Alan's phone rings (Nokia 8310) he answers it and talks to the caller yet it's obvious he isn't talking to anyone. He blatantly presses the red/cancel button to answer the call. The image hadn't been reversed though, because he pressed the exact same button to end the call.