Visible crew/equipment: When the vending machine says it will destroy Rimmer, a boom mic can be seen at the top of the screen. (00:06:05)
Visible crew/equipment: After Rimmer faints after getting drunk, a boom mic shadow can be seen on the bedsheets. (00:15:45)
Visible crew/equipment: When we first see Rimmer and Lister in the medi-bay, the camera crew can be seen in the reflection of the tv. A boom mic arm can also be seen moving. (00:16:55)
Visible crew/equipment: When Rimmer and Kryten invites Snacky to come with them to Red Dwarf, the reflection of a crewmember is visible in Snacky's head dome. (Note this is not Rimmer's reflection since there is no H).
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