Revealing mistake: When Pree shows Lister his Medi-Bay file, it is a flipped shot. Note the danger sign next to the computer. (00:27:40)
Other mistake: Rimmer's badge of rank is missing from his short sleeved uniform. All other uniforms in the series have the badge. (00:15:10)
Stasis Leak - S2-E4
Continuity mistake: When Petersen walks away from Lister with the cases, the two women follow him. In the next shot the women have swapped places. (00:17:45)
Out Of Time - S6-E6
Visible crew/equipment: When Kryten walks into the cockpit to offer Lister a beer, a boom mic can be seen at the top of the screen by Kryten's head. (00:10:05)
Visible crew/equipment: When Rimmer is speaking to Lister about how Ace Rimmer got all the breaks in his life, a boom mic can be seen in the top left of the screen. (00:24:15)
Revealing mistake: When Lister uploads his memories, the wide shot shows various videos of Rimmer in the background, but in the close up it shows a plain white screen. (00:17:55)
Continuity mistake: When the Nazi commander throws the crocodile at Ace, the yellow curtain is behind ace as he falls. In the next shot, the yellow curtain is in front of him. It is clear he did not fall through the curtain as it does not move as he hits the floor. (00:01:00)
Timeslides - S3-E5
Continuity mistake: When we see the skiers, no one is standing in front of the screen. In the next shot, Lister has appeared from nowhere. (00:07:20)
Continuity mistake: When Hollister picks up the lemon drink, his left hand is by his side. In the next shot it is on his chest. (00:01:50)
Revealing mistake: When Kochanski is shot with the spear, the padding that gives the impression the spear is through her leg is visibly bulging in her trousers as ahe pulls on the rope. (00:26:50)
Continuity mistake: When the wax droids charge at the start of the battle, Santa, Marilyn Monroe and Pope Gregory charge forward, but in the next shot, Marilyn Monroe is running on her own. (00:22:35)
Gunmen of the Apocalypse - S6-E3
Visible crew/equipment: Just after the simulant beams aboard and Lister and the Cat sit up from the table, a boom mic can be seen at the top of the screen. (00:07:40)
Gunmen of the Apocalypse - S6-E3
Continuity mistake: When Lister says the escape pod is not an option, his hands are apart in front of him. In the next shot, they are together. (00:12:20)
Emohawk - Polymorph II - S6-E4
Continuity mistake: Just before the damage report machine explodes, the room is full of smoke. As it explodes, all the smoke is gone. (00:07:40)
Visible crew/equipment: When both Rimmer and his future echo walk through the door from the captain's office, the edge of the set can be seen. (00:15:09 - 00:16:04)
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