Continuity mistake: When Kochanski is banging on the pipes at the start of the episode, she is using her right hand. There is then a close up shot of the pipe and you can see she is using her left hand. (00:01:50)
Continuity mistake: When Kochanski is in bed at the start of the episode, she is wearing stud ear rings. When she gets up to go to the kitchen area, they are now hoops. (00:02:20 - 00:03:50)
Continuity mistake: When the ducts are being backwashed, Lister's dreadlocks are on his right shoulder. But when the shot changes and he says "I hate this. I really hate this.", his locks are on his left shoulder. Then the shot changes again and they're back on his right shoulder. (00:23:53)
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