Visible crew/equipment: A boom mic shadow appears on Lister's head just after he opens the door with the severed hand. (00:19:20)
Stasis Leak - S2-E4
Continuity mistake: When Lister's double comes out of the bathroom, Lister's locks move from in front of his shoulders to behind his neck. (00:25:15)
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)
Confidence and Paranoia - S1-E5
Revealing mistake: When Rimmer gets into bed, near the start of the episode, you can see that he brushes past Lister's blanket hanging down and slightly moves it. He should not have been able to do this as he is a hologram, it should have passed through him. Rimmer's pillows and bedding move as well. (00:06:50)
Out Of Time - S6-E6
Continuity mistake: When Lister gets killed, his locks are behind his back. In the shot before, they are over his left shoulder. (00:26:20)
Continuity mistake: When Starbug gets taken over and Kryten says it is not a malfunction, he has his hands in the air. The camera cuts to Rimmer, and Kryten's hands are by his side. (00:03:45)
Continuity mistake: When Lister drops the magazine in front of Rimmer it lands closed. When Rimmer begins to read it, it is open on the floor. (00:13:25)
Stasis Leak - S2-E4
Continuity mistake: When the Cat and Lister look at the wedding photo at The End of the episode, Lister is holding the photo at the bottom left corner in some shots, and the bottom right in others. (00:23:10)
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)
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: 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: The cigarette butts that Lister supposedly tips out of his lager can were obviously in between his hand and the can, and not in the can at all. (00:19:25)
Other mistake: When the meteor hits Starbug, there are no stars outside the front of the ship at all. (00:07:20)
Visible crew/equipment: When Lister does the log at The Beginning of the episode, a boom mic shadow can be seen on his face throughout the scene. (00:00:40)
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