Quarantine - S5-E4
Continuity mistake: When Rimmer is looking at the crew through the viewscreen in Quarantine, the reflection of the crew in the glass changes between shots. (00:21:20)
Continuity mistake: When Starbug jolts for the first time, Rimmer is looking to his right. The camera cuts and he is looking forwards. (00:03:30)
Continuity mistake: At the start of the episode when we first see the polymorph, it looks into the mirror, then covers its eyes. Yet when we see the reflection, it already has its hands over its eyes before it gets to the mirror. (00:01:30)
Stasis Leak - S2-E4
Continuity mistake: At The End of the episode when Lister is talking to Holly on his watch, Lister's red sleeve is in line with the watch, but as the camera cuts to show Holly, the sleeve is gone. (00:24:10)
Continuity mistake: At the disco, when the Rimmers are seated at their table, the plant moves from in front of the lamp to behind it. (00:15:40)
Stasis Leak - S2-E4
Continuity mistake: When Lister is leaving the honeymoon suite, his locks move between shots. (00:26:25)
Confidence and Paranoia - S1-E5
Continuity mistake: When Lister is in the Medi-bay, he has his duvet on his lap. The angle changes and he has the duvet over his shoulders. (00:12:30)
Continuity mistake: When Lister punches up the Leviathan's destination, it reads 'Theta 4'. However, in the next scene in Starbug's medibay, Lister says that the Leviathan was headed to Delta 7. (00:23:10 - 00:24:25)
Continuity mistake: Kryten removes the polymorph underpants and throws them under the covers of Lister's bed. When he checks the bed and pulls out a snake the pants are now on top of the covers (even though he says they're gone) and the covers themselves are now arranged differently. (00:10:00)
Continuity mistake: At The End of "Nanarchy" Starbug 1 flew underneath Starbug 2 at The End of the episode, yet in this episode when the scene is repeated, the ship flies around Starbug 1 instead. (00:05:50)
Continuity mistake: When Ace crashes into the boxes, Kryten's left elbow is in front of the Cat. In the next shot it is by his side. (00:28:00)
Continuity mistake: When Lister is fixing his robot goldfish, he picks it up with his right hand, then after the camera cuts, he puts it back into the tank with his left hand. (00:06:00)
Continuity mistake: When the virus starts to eat the potatoes, Rimmer picks them up from the pile just below eye level. In the wide shot it shows the potatoes are just below waist level and Rimmer would have had to lean much further away from where he was standing to get the potatoes from that height. (00:20:00)
Emohawk - Polymorph II - S6-E4
Continuity mistake: When Lister gives the Gelf the cigar, he looks over his shoulder at Kryten. In the next shot, he looks over his shoulder again. (00:11:50)
Continuity mistake: When the crew almost kill themselves, Kryten is holding the harpoon gun to his head. The point of the spear is missing but in the next shot it has reappeared. (00:23:30)
Continuity mistake: In the disco when Lister complains about the female Lister's attempts to impress him, his hair is in front of his left shoulder, then behind it. (00:19:10)
Continuity mistake: When Lister sees the future echo in the drive room, Rimmer points when he says 'Shut up.' However when the scene plays out again, Rimmer's arms stay down by his sides. (00:15:00 - 00:16:00)
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