Continuity mistake: When Lister is explaining the ending of the movie, he says "It's about a dude who sacrifices his life for love" whilst Rimmer looks at him, but in the next shot, Rimmer is suddenly looking forwards before turning back to Lister saying "as if." (00:02:55)
Continuity mistake: After Rimmer and Nirvanah have sex, as they're getting out of bed, Nirvanah ties her robe twice. In the next shot as she's standing, the robe is open again. (00:14:00)
Continuity mistake: When Kryten tells Rimmer he doesn't have the brain that can accept an implant, he says "No" and begins walking around the table. Kryten has his hands raised with his right hand slightly lower than the left, but in the next shot, both hands are suddenly level with each other. (00:22:05)
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