Other mistake: At the start of Rimmer's exam, the invigilator orders the students to "turn over their papers and start". Rimmer reads one side of the paper, then turns it over to read another question. The back of the paper should have been blank as otherwise there would be no point asking the students to keep the papers face down before reading the questions. (00:15:30)
Other mistake: When the Cat says there better be no dogs on the ship, there are only about two or three stars visible out the window. Far too few given the amount of stars shown in exterior space shots of the ship. (00:05:15)
Other mistake: When Rimmer is doing Lister's memo, there there are only about a few stars visible out the window, which is far too few given the amount of stars shown in exterior space shots of the ship. Additionally, a star suddenly appears in the window. (00:23:15)
Other mistake: Rimmer's badge of rank is missing from his short sleeved uniform. All other uniforms in the series have the badge. (00:15:10)
Other mistake: In the picture of the cat wars between the Red Hats and the Blue Hats, the hats are orange instead of blue. (00:19:00)
Other mistake: The Cat Priest has no fangs when every other Felis Sapiens has them.
Other mistake: When Lister reads Rimmer's diary, he reads the first entry, then his aunt's birthday in July and then the entry for Gazpacho Soup Day in November. Each time he looks for the next entry he flicks though the pages, yet every time he reads, it is from the start of the diary. (00:15:25)
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