Visible crew/equipment: When Binks arrives on Starbug, a boom mic can be seen at the top of the screen. (00:07:45)
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)
Plot hole: Allman does not remember his trial when The Inquisitor erases him, yet Lister and Kryten do remember their trial when they are sentenced. (00:01:20 - 00:13:30)
Continuity mistake: When the second version of Allman appears, he has his arms folded. In the next shot, they're down by his side. (00:01:25)
Visible crew/equipment: At the start of the episode, when Lister and Kryten talk about Lister's comic, a boom mic shadow can be seen on Kryten's head. (00:02:10)
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