Continuity mistake: When Lister swings the axe at The Cat and hits the door frame, the axe head bends. When Lister pulls the axe out, its head is fine again. (00:22:30)
Continuity mistake: Just before Kryten chloroforms Lister, Lister's locks jump from behind his back to over his left shoulder between shots. (00:23:40)
Continuity mistake: During the Higher Cat and Rimmer's dance when Kryten says 'and agony in torment' his arms are by his sides. In the next shot, his right arm is raised. (00:11:40)
Continuity mistake: After the Cat incapacitates Lister, the Cat complains about his collar being untidy, then steps aside. The next shot shows Lister stood on his own and the Cat is not visible at all. There was no time for the Cat to walk that fast between shots. (00:23:20)
Continuity mistake: When Lister is choking the Cat, he says 'give me a break, Rimmer'; at this point Rimmer is looking at the Cat and Lister, yet in the next shot he is looking at Kryten. (00:22:50)
Continuity mistake: The bottle of chloroform Kryten uses to take Lister by surprise appears from nowhere. (00:23:30)
Continuity mistake: When Lister, the Cat and their higher selves are walking down the corridor, the way Lister is facing changes between shots throughout the scene. (00:09:30)
Continuity mistake: When remote controlled Lister is strangling the Cat, his locks are partially over his left shoulder and partially behind his back. When Lister picks up the bazookoid, his locks are all over his left shoulder. (00:23:10)
Continuity mistake: When Lister is sent flying when the crates explode, his hat falls off, but when he sits up he is still wearing it. It then falls off again when the low Lister spits at him, yet he is still wearing it when he rolls away. (00:13:50)
Continuity mistake: When the low Kryten takes the spinal implant from low Lister, he uses his right hand. In the next shot, the implant has switched hands as Kryten uses his right hand to lift up Lister's head. (00:16:40)
Continuity mistake: When Lister crushes the high Rimmer's light bee, he puts his arm into Rimmer's chest. In the next shot, Lister's arm is gone. (00:21:35)
Continuity mistake: When Starbug bursts out of Red Dwarf, the shot from behind shows Starbug spinning in circles, but the shot from in front shows Starbug flying normally. (00:04:00)
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