
Rimmerworld - S6-E5
Visible crew/equipment: When Rimmer argues that they should not board the simulant ship, the shot of Lister in the foreground and Rimmer in the background shows a boom mic just above Rimmer's head. (00:04:40)
Rimmerworld - S6-E5
Visible crew/equipment: When Starbug goes through the wormhole, a boom mic shadow can be seen on the back wall next to Kryten. (00:20:20)

Rimmerworld - S6-E5
Visible crew/equipment: When Lister, the Cat and Kryten arrive on Rimmerworld, as the Rimmer guard steps out and says 'silence mutant' a boom mic is visible at the top of the screen. (00:21:05)
Rimmerworld - S6-E5
Visible crew/equipment: In the cell, when Rimmer says 'What have I created?' in the next shot a boom mic can be seen at the top of the screen by the window. (00:25:50)
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