Visible crew/equipment: When the crew are standing before the Judgement computer (when Lister is worrying that he will be sent to prison) if you look above Lister's head you can see a microphone bob up and down into shot. (00:11:10)
Revealing mistake: When the Dalai Lama explodes, there is a single shot where he has disappeared and a yellow cloth has taken his place just before the explosion. The cloth then lands in the background. (00:22:55)
Visible crew/equipment: When Ace Rimmer is talking to Mellie, a boom mic can be seen at the top of the screen. (00:04:05)
Revealing mistake: When Ghandi explodes, there is a single shot where he had disappeared before the explosion goes off. (00:22:35)
Continuity mistake: When Rimmer's mother is talking to him while he is hung upside down, she is stood about a foot away from him in one shot, then in the next she is about three feet away. (00:01:45)
White Hole - S4-E4
Continuity mistake: Kryten takes the computer slug out of the machine with his left hand yet in the next shot it is in his right hand. (00:20:00)
Answer: The cello is a large four-stringed instrument, which, when it is played, stands vertically on the floor between the player's legs (assuming they are seated). If it is to grow as large as the other instuments mentioned will, it would require a rather unseemly lack of femininity to be able to encompass it with the legs.
Rooster of Doom