Rimmerworld - S6-E5
Revealing mistake: When Rimmer kisses the female Rimmer, the scar on his cheek disappears. (00:22:30)
Out Of Time - S6-E6
Visible crew/equipment: When the Cat becomes visible again after going through an unreality pocket, the shot changes to a wide shot of the crew. A boom mic can be seen to be pulled out of shot at the top of the screen by Kryten's head. (00:11:40)
Revealing mistake: When Legion gets hit, you can see his real face for a second when he adjusts his mask. (00:21:30)
Out Of Time - S6-E6
Visible crew/equipment: When Kryten bends down to pick up the xrays, a boom mic shadow can be seen on the top of his head. (00:05:00)
Emohawk - Polymorph II - S6-E4
Visible crew/equipment: When Rimmer says the oxy-generation unit is destroyed, a boom mic shadow can be seen on the crate in front of him. (00:09:40)
Out Of Time - S6-E6
Visible crew/equipment: In the scene just befoe Lister & the Cat go into stasis, a boom mic shadow can be seen moving on the desk in front of Rimmer. (00:12:20)
Rimmerworld - S6-E5
Continuity mistake: At The End of the episode, when Lister says, 'I'm saying nothing man, don't want to spoil the surprise,' his hood and locks are arranged completely different than all other shots in the scene. (00:27:20)
Out Of Time - S6-E6
Visible crew/equipment: When Kryten walks into the cockpit to offer Lister a beer, a boom mic can be seen at the top of the screen by Kryten's head. (00:10:05)
Emohawk - Polymorph II - S6-E4
Visible crew/equipment: After the crash when Lister comes in from outside, as he says 'it's waist high out there', a boom mic can be seen at the top of the screen. (00:09:30)
Out Of Time - S6-E6
Visible crew/equipment: At the start of the episode when Rimmer says 'any objections?' a boom mic can be seen moving across the top of the screen. (00:01:25)
Continuity mistake: When Legion brings the feast, Kryten is stood by the door. Rimmer says about how he appreciates art, then in the next shot of the Cat, Kryten walks behind him. Kryten would have had to walk past Rimmer in the previous shot to get there yet we did not see him while Rimmer was talking. (00:13:15)
Gunmen of the Apocalypse - S6-E3
Revealing mistake: When the crew are trying to figure out how to save Kryten before going into the game, the Cat says 'if not, why not?' You can see Lister mouth the line. (00:15:25)
Gunmen of the Apocalypse - S6-E3
Continuity mistake: When Lister leaves the saloon, his gloves appear on his hands between shots as he goes outside. (00:21:45)
Gunmen of the Apocalypse - S6-E3
Visible crew/equipment: Just after the simulant beams aboard and Lister and the Cat sit up from the table, a boom mic can be seen at the top of the screen. (00:07:40)
Gunmen of the Apocalypse - S6-E3
Continuity mistake: When the Apocalypse boys shoot the bottle out of Kryten's hand, you can see Kryten drop the bottle neck. In the next shot he is still holding it. (00:14:45)
Gunmen of the Apocalypse - S6-E3
Revealing mistake: When Rimmer throws a cowboy over the bar, it wobbles. (00:21:35)
Gunmen of the Apocalypse - S6-E3
Continuity mistake: When the Cat realises he has lost his special skills, Lister is looking straight forwards. In the next shot he is looking down at the ground. (00:24:50)
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