Continuity mistake: When Kochanski puts the cat in the disintegrator, it changes the way it's facing between shots and again when she takes it out. (00:11:19)
Revealing mistake: When Kochanski is on the phone falling through space, her lips do not match what she is saying. (00:25:55)
Visible crew/equipment: In the medi-bay after Kochanski is shot, a white boom mic is visible in the top right corner as she tries to get up. (00:27:30)
Revealing mistake: When Kochanski is shot with the spear, the padding that gives the impression the spear is through her leg is visibly bulging in her trousers as ahe pulls on the rope. (00:26:50)
Revealing mistake: When the ship crashes into the snow planet, a wire can be seen attached to it as it crashes.
Continuity mistake: When the crew meet the alternate dimension crew, both crews are standing side by side, but when the two Listers shake each other's hands, the Cat and Kryten from both crews have disappeared.
Continuity mistake: In the Aigburth Arms, when Frank hands the box with baby Lister to the barmaid, the barmaid takes the box placing her hand on top of the box, but in the next shot, her hand is suddenly on the side of the box.
Continuity mistake: When hologram Lister has finished explaining to the crew why he is dead, the crew are standing side by side, but when Lister asks what happened to Kochanski, Cat and Kryten have vanished.
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