Continuity mistake: When the Cat asks if fish swim south for the winter, Kryten is looking at him. In the next shot, as Kryten answers, Kryten is looking up and away from the Cat. (00:02:05)
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)
Quarantine - S5-E4
Revealing mistake: When Lanstrom corners Lister, Kryten and the Cat, she is holding onto the fence. As she is a hologram, this would be impossible. (00:10:10)
Quarantine - S5-E4
Continuity mistake: Just before Dr. Lanstrom appears, Kryten is standing behind Lister. In the next shot, he has moved much further away from him, then moves back and forth between shots. (00:06:40)
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)
Visible crew/equipment: When we first see the crew looking at the radar before the lights go out, a boom mic can be seen in the top left corner of the screen. (00:05:35)
Quarantine - S5-E4
Visible crew/equipment: When Rimmer asks the crew if they had forgotten Red Dwarf could only sustain one hologram, it shows a shot of the rest of the crew who say nothing. At the top of the screen, a boom mic can be seen. (00:03:00)
Terrorform - S5-E3
Continuity mistake: When Rimmer gets his robe torn off, he is looking forwards. In the next shot he is looking down. (00:11:00)
Continuity mistake: When The Inquisitor jumps Kryten from behind, he used both hands. In the next shot he is only using one hand to hold him. (00:14:05)
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)
Terrorform - S5-E3
Visible crew/equipment: When Lister and the Cat type into the computer, in the shots of their reflections, the lens of the camera can be seen reflected between them. (00:05:00)
Quarantine - S5-E4
Audio problem: When Dr. Lanstrom says hello into the walkie talkie, her lips do not move. (00:08:40)
Visible crew/equipment: When the crew leave the Red Dwarf game area, a boom mic is visible in the top right hand corner. (00:11:35)
Visible crew/equipment: When the Cat shoots the locker which the low Lister is hiding at The End of the episode, a boom mic can be seen above the Cat. (00:25:40)
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)
Visible crew/equipment: At The End of the episode, when Kryten explains why the Cat would kill himself, a boom mic shadow can be seen moving across his face,. (00:24:55)
Revealing mistake: During the car chase, the box Rimmer is sitting on keeps moving. (00:21:25)
Visible crew/equipment: When Holly says she is broadcasting on a higher frequency, when the crew are about to commit suicide, a boom mic can be seen in the top left of the screen. (00:23:30)
Continuity mistake: When the crew are looking at the radar, Lister's locks are in front of his shoulder on the radar cam, but behind his back in all other shots. (00:05:50)
Visible crew/equipment: Just after Lister says the despair squid will either kill them, eat them or hump them, a boom mic shadow can be seen moving on his face. (00:06:05)
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