The Long Legs of the Law - S2-E1
Revealing mistake: At the very beginning of the episode, Leonard Pearce is waiting for the cue for his character to start looking for his teeth. He's standing in the living room, between his room and Del and Rodney's room. (00:00:25)
Revealing mistake: At the point where someone gets a small bruise on the upper arm, the crew are all in a pile and thrashing about on the floor. There are 5 pairs of legs instead of 4. Arthur is in his pajamas, Zaphod is in orange trousers, Trillion is lying on top of Ford and Ford is too far away for them to be his legs. [The fifth pair of legs belong to the person playing zaphod's third arm - doesn't mean it's not a mistake, but that's where they come from.]
Revealing mistake: When Edward opens the gate to let Tracy in, we then see a shot of Tracy and you can see it is repeated footage of her from when she met Edward for the first time.
Revealing mistake: After Lentius stabs Silva, the knife blade Lentius used bends and wobbles as it is thrown to the ground.
The Two-Hundred-Mile-an-Hour Fastball - S2-E1
Revealing mistake: During Ralph's tryout for the team, when the catcher yells, "Come on, skinny bones, try to put one right there...," the stunt wire is visible behind the catcher in this shot as well as the following shot, when he flips over. (00:10:10)