Continuity mistake: When Holly interrupts Rimmer learning Esperanto saying "The menu looks interesting", he appears on the TV screen, with his chin blocked by the edge of the frame. The shot then cuts to a view of the screen, and his entire face is suddenly fully in the frame. (00:05:00)
Continuity mistake: When Lister is getting ready, he pulls his trousers off the table, causing the boot on the table to wobble. In the next shot, the boot is entirely still. (00:10:35)
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