Confidence and Paranoia - S1-E5
Continuity mistake: When Confidence is telling Lister that his song was the greatest love song ever, Lister has his right hand on his lap, but in the next shot, his right hand is suddenly on the guitar strings. (00:19:35)
Revealing mistake: When Rimmer runs to Lister after Lister unsuccessfully orders a black coffee, the camera tilts.
Revealing mistake: When Lister goes to Rimmer's room the second time, the door opens before Lister hits the switch.
Other mistake: Rimmer's badge of rank is missing from his short sleeved uniform. All other uniforms in the series have the badge. (00:15:10)
Continuity mistake: When the Cat leaves Lister's quarters after showing him the cat book, one of Lister's locks is hanging over his right shoulder. In the next shot it is gone. (00:11:40)
Confidence and Paranoia - S1-E5
Continuity mistake: When the Cat visits Lister, Lister puts his arm down on the bed, but in the next shot he is leaning on his hand. (00:14:45)
Confidence and Paranoia - S1-E5
Continuity mistake: When Lister and Confidence go outside the ship, they do a little dance and both put their right feet forwards. In the next shot, their left feet are forward as they continue the dance. (00:25:30)
Continuity mistake: When Lister goes into stasis, Todd Hunter turns the wheel on the door to lock Lister in. In the next scene when Lister awakes from stasis, he just pushes the door open without turning the wheel to unlock it. Even if we are to assume that Holly would automatically open the door, the wheel should still turn to unlock the mechanism.
Other mistake: The Cat Priest has no fangs when every other Felis Sapiens has them.
Visible crew/equipment: When both Rimmer and his future echo walk through the door from the captain's office, the edge of the set can be seen. (00:15:09 - 00:16:04)
Continuity mistake: When Rimmer stresses out while preparing for his exam, he puts his hands on his face, and screams whilst starting to bend over. In the next shot, Lister wakes up, and Rimmer is suddenly standing upright. (00:13:20)
Visible crew/equipment: When Lister steps back inside the observation room after Rimmer leaves, a stage light can be seen reflected in the window-like light fixture on the wall. It can't be a light on the ship as none of the lighting on Red Dwarf is in the shape of the light seen in the reflection. (00:14:05)
Revealing mistake: When the future echo Rimmer leaves the drive room and the actual Rimmer walks in, there is a visible line caused by the split screen effect, done to show two Rimmers onscreen at the same time.
Continuity mistake: When Rimmer first realises that his files are unflattering, the screen first from the right on the computer bank shows writing. But a change of view later, Holly is on the same screen. He does not have time to move.
Confidence and Paranoia - S1-E5
Revealing mistake: When Confidence is trying to get Lister to take his helmet off, Lister climbs over a railing and jumps around him. It is clear that the footage of Lister jumping around was slowed down to make his movement appear as if there is a lack of gravity. (00:26:35)
Other mistake: When Rimmer is doing Lister's memo, there there are only about a few stars visible out the window, which is far too few given the amount of stars shown in exterior space shots of the ship. Additionally, a star suddenly appears in the window. (00:23:15)
Other mistake: When the Cat says there better be no dogs on the ship, there are only about two or three stars visible out the window. Far too few given the amount of stars shown in exterior space shots of the ship. (00:05:15)
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