Continuity mistake: Lister's rolling pin is dirty with flour when Christine walks in, but when Lister turns around, it's clean. Then it's dirty two seconds later, and then disappears completely after Lister drops the bowl. (00:26:12)
Visible crew/equipment: Just after Lister hits the toaster, a pair of legs can be seen moving in it's reflection a moment before the scene ends. (00:11:30)
Out Of Time - S6-E6
Revealing mistake: When the crew wake up from stasis, there is a model shot of Starbug flying towards the epicentre. You can see the legs of Starbug partially disappear as it gets closer to the ship. (00:12:45)
Rimmerworld - S6-E5
Continuity mistake: During the hold-up scene with the Simulant, in the close-up of her speaking, her face is in darkness. The camera cuts away to Rimmer running for the escape pod, and then back to the Simulant, who is now well lit by a pair of overhead lights. (00:12:10)
Continuity mistake: During Ace Rimmer's funeral, the blow up doll is not visible earlier in the scene next to the Cat, but then appears from nowhere. (00:24:50 - 00:25:40)
Stasis Leak - S2-E4
Continuity mistake: When Lister's double says 'You don't look pleased to see me' his locks move from over his shoulder to down his back and they continue switching during the scene. (00:25:30)
Out Of Time - S6-E6
Visible crew/equipment: When Lister gets killed, a boom mic can be seen on the very far right of the screen next to Rimmer. (00:26:25)
Other mistake: At the start of the episode, there is a spoof Star Wars-type caption, which spools up the screen very quickly. Too quickly to be read, in fact... which may explain why few people have noticed that the last line of the caption, "And now the Saga Continuums...", is written twice. (00:00:20)
Revealing mistake: When Lister leaves for his exam, he walks through Rimmer. As he does, both Rimmer and Lister become transparent when it should have just been Rimmer. (00:25:50)
Other mistake: When the meteor hits Starbug, there are no stars outside the front of the ship at all. (00:07:20)
Continuity mistake: When The Cat does his dance with Blue Midget, he stands behind one of the legs of Blue Midget and changes his clothes. The old clothes he throws on the ground when changing disappear in the wide shot of the landing area. (00:08:55)
Continuity mistake: When Lister puts his Better Than Life helmet on, the cable is hanging over his right shoulder. In the next shot it is hanging down over his left shoulder. (00:15:45)
Continuity mistake: When the bike appears on the beach, the front tyre is above the level of sand. In the next shot it has sunk by about an inch. (00:17:50)
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