Continuity mistake: During the Higher Cat and Rimmer's dance when Kryten says 'and agony in torment' his arms are by his sides. In the next shot, his right arm is raised. (00:11:40)
Revealing mistake: When the simulant pulls the knife out of his chest, you can see the knife is a dummy. As the handle is pulled back, the blade does not move at all. (00:25:30)
Continuity mistake: When the Cat dances at the disco, he jumps up and grabs the mirror ball with both hands. In the next shot he is only holding it by one arm. (00:20:25)
Stasis Leak - S2-E4
Continuity mistake: When Lister first walks through the Stasis Leak, his locks are over his left shoulder, then in the bathroom they are over both shoulders. (00:09:30)
Other mistake: When Rimmer tries to silence the vending machine, he covers up the input microphone with stickers instead of covering the speaker just above it. (00:05:05)
Continuity mistake: A door has appeared in the main living area of Starbug that was not there in previous episodes. (00:01:50)
Out Of Time - S6-E6
Continuity mistake: When the crew fire at their future selves, Lister says 'locking on, firing'. His locks are behind his back but in the next shot they are in front of his left shoulder. (00:26:10)
Revealing mistake: The low Cat's teeth move and wobble in ways they should not be able to when he is first seen. (00:14:10)
Terrorform - S5-E3
Continuity mistake: Just after one of the hooded legions reads from the scroll, he manages to turn around and face the opposite direction in one camera cut. (00:10:45)
Terrorform - S5-E3
Visible crew/equipment: A boom mic shadow can be seen along the bottom of the screen when the crew have to leave Starbug and walk. (00:11:25)
Terrorform - S5-E3
Visible crew/equipment: When Lister, Cat and Kryten leave the cockpit with the plan to make Rimmer feel good about himself to escape, a boom mic can be seen in the top left corner of the screen. (00:22:45)
Continuity mistake: Lister says his ID code is Lister-D-00169, yet in Furture Echoes he gave it as RD-52169. (00:14:55)
Visible crew/equipment: At the start of the episode, when Lister and Kryten talk about Lister's comic, a boom mic shadow can be seen on Kryten's head. (00:02:10)
The Last Day - S3-E6
Continuity mistake: When Kryten throws away the breakfast, Lister's locks move from behind his shoulder to in front of it in a single cut. (00:01:55)
Continuity mistake: When Lister is changing near the start of the episode, there are no stickers on his locker. When he leaves the room, they appear. (00:03:55 - 00:05:10)
Confidence and Paranoia - S1-E5
Revealing mistake: Rimmer asks Confidence and Lister "Where's Paranoia?", when Confidence replies "I dont know. Is it some place near Uruguay?" Lister is mouthing his lines. (00:24:50)
Continuity mistake: After Rimmer and Nirvanah have sex, as they're getting out of bed, Nirvanah ties her robe twice. In the next shot as she's standing, the robe is open again. (00:14:00)
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