Visible crew/equipment: When Zaphod says his first line "I certainly didn't survive.", you can see the person who plays his third arm standing behind him.
Big Brother - S1-E1
Continuity mistake: At the start of the episode when Del walks behind Grandad's chair, the way he is holding his jacket changes between shots. (00:01:15)
There's Just No Accounting... - S2-E18
Revealing mistake: After Ralph tells Bill that the kidnappers are planning to take another child, when Bigsby walks out of the Sherwin house, in the next shot just as Ralph flies off we can see the stunt's springboard between the bush and the tree. (00:31:05)