Quarantine - S5-E4
Continuity mistake: When Kryten injects the luck virus into Lister's neck, the gun disappears from Kryten's hand between shots. (00:23:25)
Quarantine - S5-E4
Continuity mistake: After Lister gets the luck injection for the first time, he is holding his hat. In the next shot the hat is gone. (00:12:15)
Quarantine - S5-E4
Continuity mistake: When Rimmer is looking at the crew through the viewscreen in Quarantine, the reflection of the crew in the glass changes between shots. (00:21:20)
Quarantine - S5-E4
Continuity mistake: When Lister gets the second luck virus injection, his locks move from in front of his shoulder to behind his back. (00:23:25)
Quarantine - S5-E4
Continuity mistake: Just before Dr. Lanstrom appears, Kryten is standing behind Lister. In the next shot, he has moved much further away from him, then moves back and forth between shots. (00:06:40)
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