Timeslides - S3-E5
Revealing mistake: When Lister is hit in the face with the snowball, some of the snow lands on Rimmer's hologramatic uniform. (00:07:40)
Timeslides - S3-E5
Revealing mistake: When Rimmer dies at The End of the episode, a dummy is visible just before the explosion. (00:26:40)
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