Other mistake: When Kryten and Camille are having dinner, Camille puts her "hand" in the soup and begins slurping it up. The level of soup remains the same and doesn't lower despite being slurped. (00:22:25)
Continuity mistake: When Camille asks Kryten if they could make it, Kryten puts his glass down on the table. In the next shot, it is suddenly back in his hand, being put back down again. (00:22:35)
Visible crew/equipment: When Lister and the Cat are walking through the corridor on the ship, the top of the set is visible through the transparent ceiling. (00:03:55)
Continuity mistake: Lister enters with a tray with some food on to give to Kryten. The position of the tray changes position between shots. (00:10:10)
Continuity mistake: In the scene where Lister is talking to human Kryten, just before Lister sees the photos, keep an eye on Lister's hat. It is perched on top of his head with about an inch of hair showing, yet the next shot shows the hat covering all of the hair, then it goes back to an inch of hair showing again. There is no time for Lister to have adjusted his hat between cuts. It is clear the line had to be re-shot. (00:12:35)
Continuity mistake: Kryten has three spare heads but in 'The Last Day' in series 3, he only packed away one head. (00:18:40)
Revealing mistake: The metal shelf the three spare heads sit on can be seen to move as spare head three speaks. (00:19:40)
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