Visible crew/equipment: Just before Red Dwarf explodes, there is a shot of Lister. In the background you can see a moving shadow of a crew member on the floor. (00:04:25)
Visible crew/equipment: When the High Rimmer and Cat dance, in the wide shot a boom mic can be seen at the top of the screen. (00:11:35)
Visible crew/equipment: After Lister is attacked by low Kryten, he sneaks through the cargo bay. There is a shot where the camera is following Lister as he sneaks around a corner, if you look at the floor you can see the shadow of the cameraman. (00:14:45)
Visible crew/equipment: When the Cat shoots the locker which the low Lister is hiding at The End of the episode, a boom mic can be seen above the Cat. (00:25:40)
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