Continuity mistake: The time that the events involving the crew of Red Dwarf keeps changing throughout the series. At various times, references are made to the date, which is stated as being in the 21st, 22nd or 23rd centuries. Examples: In 'Stasis Leak', the date reference is stated as being 2077 (21st century). But in 'Ouroboros', the date is stated as being 26th November 2155 (22nd century). Also in 'DNA', Lister says he is an enlightened 23rd century guy.
Deliberate mistake: In the first few series, it is suggested Lister and Kochanski barely know each other. In 'Balance of Power' Holly says that Lister has only ever spoken 173 words to her. However, by series 4 Kochanski is referred to as Lister's ex-girlfriend with whom he shared a relationship. In the series 4 documentary, Doug Naylor explains that Lister's attitude towards Kochanski was immature in the first series which is why they changed his back story from wanting to be with Kochanski to actually having been with her by series 4.
Other mistake: Unfortunately the whole basis of the show is one big factual error. Throughout the series we see that Red Dwarf sustains damage from collisions, explosions, and so on. Most important of all, the rocket engine nozzle - surely made from the strongest materials available - has been punctured by some kind of impact. The systems require constant maintenance by humans (painting, repairs, etc), so skutters are not enough by themselves. So, we know that Red Dwarf is not made of some sort of fictional, indestructible materials, it is made of the kind of metals, plastics and other construction materials we build space shuttles and the like out of nowadays. So, after three thousand - never mind three million! - years the whole ship would be a clump of useless, corroded junk. The rubber and plastics in seals, electronic components and furniture would have crumbled to powder. The electronics themselves would have failed after a few hundred years at most. Metals in contact with liquids in pipes or reservoirs would have oxidized, and even the oxygen in the air would have been corrosive after that amount of time. Red Dwarf is not immune from the effects of long term decay and deterioration - if it were when Lister was released from stasis he would have found rooms full of relatively intact dead bodies instead of piles of crumbled dust. After three million years in space Red Dwarf would have been a pile of scrap, fatal to anyone going near it; subject to slow, subtle but constant radioactivity in space, after three million years it would be hotter than the inside of a working reactor.
Other mistake: Throughout the show, reference is made to Rimmer's light-bee, a solid unit that buzzes around projecting his holographic image. Yet he constantly walks through things without any difficulty. Not physically possible if there is something solid in his form.
Other mistake: Holograms are often seen passing through physical objects, walls, furniture, and other people. Yet, they have a physical object generating the hologram: their light-bee. This would not be able to pass through other solid objects.
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