Quarantine - S5-E4
Continuity mistake: When Kryten injects the luck virus into Lister's neck, the gun disappears from Kryten's hand between shots. (00:23:25)
Quarantine - S5-E4
Continuity mistake: When Lister gets the second luck virus injection, his locks move from in front of his shoulder to behind his back. (00:23:25)
Quarantine - S5-E4
Revealing mistake: When Lister uses the keypad to escape from Quarantine, more button lights turn off than he has actually pressed. (00:23:35)
Continuity mistake: When Starbug bursts out of Red Dwarf, the shot from behind shows Starbug spinning in circles, but the shot from in front shows Starbug flying normally. (00:04:00)
Visible crew/equipment: Just before Red Dwarf explodes, there is a shot of Lister. In the background you can see a moving shadow of a crew member on the floor. (00:04:25)
Character mistake: After the crew realise that the matter paddle has made 2 copies of Red Dwarf, Kryten says something along the lines of, "When I threw the machine in reverse...", but it wasn't actually him who threw the machine in reverse, it was Lister. (00:06:55)
Revealing mistake: After Starbug lands on the 'high' Red Dwarf, Rimmer is running out of power and starts to fade in and out. However, Cat, who must be standing too close to Rimmer also fades, the backdrop being partially visible through him. (00:08:05)
Continuity mistake: When Lister, the Cat and their higher selves are walking down the corridor, the way Lister is facing changes between shots throughout the scene. (00:09:30)
Audio problem: When the high Lister plays the harp, his fingers are out of sync to what is being played. (00:11:30)
Visible crew/equipment: When the High Rimmer and Cat dance, in the wide shot a boom mic can be seen at the top of the screen. (00:11:35)
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: The pyrotechnic charges are visible under the 'High' Cat and Kryten's robes, before they are shot. There is also a wire trailing behind Kryten and running up his left leg, presumably a means of detonating the charges. (00:12:45)
Audio problem: When the high Kryten picks up the bomb, the high Cat can be seen to start speaking but no sound is heard. In the next shot, the high Cat is then smiling. (00:13:30)
Continuity mistake: When Lister is sent flying when the crates explode, his hat falls off, but when he sits up he is still wearing it. It then falls off again when the low Lister spits at him, yet he is still wearing it when he rolls away. (00:13:50)
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)
Visible crew/equipment: After Lister is attacked by low Kryten, he sneaks through the cargo bay. There is a shot where the camera is following Lister as he sneaks around a corner, if you look at the floor you can see the shadow of the cameraman. (00:14:45)
Continuity mistake: When the low Kryten takes the spinal implant from low Lister, he uses his right hand. In the next shot, the implant has switched hands as Kryten uses his right hand to lift up Lister's head. (00:16:40)
Revealing mistake: When Lister slams his nose into the door of the cabinet, you can see it is nowhere near it. (00:17:50)
Continuity mistake: When Lister crushes the high Rimmer's light bee, he puts his arm into Rimmer's chest. In the next shot, Lister's arm is gone. (00:21:35)
Continuity mistake: When Lister swings the axe at The Cat and hits the door frame, the axe head bends. When Lister pulls the axe out, its head is fine again. (00:22:30)
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