Visible crew/equipment: When Lister is putting the chicken vindaloo on the table, a stage light is visible on the left hand side of the screen. (00:11:50)
Visible crew/equipment: In the Captain's Office, when Rimmer says "That is not true. We played the joke on Mr. Ackerman, sir", a stage light is reflected on the object behind him and Lister. (00:01:05)
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