Gunmen of the Apocalypse - S6-E3
Visible crew/equipment: At the start of the episode when Rimmer says they should surrender, a boom mic is visible at the top of the screen. (00:06:10)
Gunmen of the Apocalypse - S6-E3
Visible crew/equipment: Just after the simulant beams aboard and Lister and the Cat sit up from the table, a boom mic can be seen at the top of the screen. (00:07:40)
Gunmen of the Apocalypse - S6-E3
Visible crew/equipment: When the simulant has beamed on board Starbug, Lister and The Cat get up slowly from the table. Look closely, and you can see the shadow of a boom mic cast on Lister and The Cat. (00:07:50)
Gunmen of the Apocalypse - S6-E3
Visible crew/equipment: When sheriff Kryten asks for a drink, a boom mic can be seen at the top of the screen. (00:13:55)
Gunmen of the Apocalypse - S6-E3
Visible crew/equipment: After Rimmer is sick, as Lister comes to his rescue, a boom mic shadow can be seen on the wall behind them near the horns. (00:18:50)
Gunmen of the Apocalypse - S6-E3
Visible crew/equipment: When the crew's special skills get erased, a boom mic shadow can be seen on Lister. (00:24:20)
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