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.]
Reseda Rose - S1-E6
Continuity mistake: When Ralph is flying to Simpsons house, he continuously flies over the same area 5 to 6 times...meaning it is just reused footage. (00:20:50 - 00:21:40)
Character mistake: No referee in wrestling would allow a double team to occur without either trying to break it up or counting to five. Yet here he allows The Golden Girls to do so twice.
Visible crew/equipment: When Miss Hawk is speaking to Edward by the well, the boom mic can be seen in the top right of the screen.