Trivia: When the crew of Starbug have to decide which of the two "Dave Listers" aboard is the real thing, they line both up for a test of their guitar playing ability. One "Dave Lister" plays a blistering, dazzling, guitar solo; the other plays dreadfully. The rest of the crew immediately know that the one that played the guitar brilliantly is the 'fake'. (Dave Lister only THINKS he can play guitar well - in fact he's hopeless at it.). The hands that we see playing the 'brilliant' guitar solo belong to "Roxy Music" guitarist Phil Manzanera. (Grant Naylor had originally wanted to get 'Queen' guitarist Brian May to play the solo, but he wasn't available).
Trivia: Rob Grant and Doug Naylor originally tried to get Brian May to film the guitar solo scene, but he was unavailable. However, Anita Dobson (May's wife) asked if there was a part for her, and she was given the part of Captain Tau. The writers have since said if they'd known she was interested they would have written her something more substantial.
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