Revealing mistake: During the chase on the moon, there is a shot from in front of Starbug crashing into an asteroid. About twenty seconds after this, the exact same shot of Starbug crashing into an asteroid is been repeated a second time, when the ship crashes. (00:23:20)
Revealing mistake: Starbug and Blue Midget wobble on a number of occasions during the chase. (00:23:25)
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)
The Last Day - S3-E6
Revealing mistake: You can tell Robert Llewellyn is reading his lines when Kryten receives the computer chip. He is looking much lower than the chip in his hand and it was obviously quite a complicated piece of dialogue to remember. (00:12:35)
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