Visible crew/equipment: When Lister washes his face in his sleeping quarters, Rimmer is seen off set in the reflection in the fish tank walking past. You can see his uniform and can just make out the H on his forehead. (00:04:40)
Visible crew/equipment: In the flashback scene of Lister and his mates, just after Lister says about brains in jars, a yellow boom mic can be seen at the top of the screen. (00:06:00)
Revealing mistake: When the Cat is pushing the trolly of cigarettes, Rimmer walks past him and bangs his arm against it. (00:09:30)
Continuity mistake: When Lister and Rimmer are talking in their bunks, Lister says 'I've always been crazy about her'. He is looking to his right with his arm in the air, yet in the next shot he is looking down at the floor. (00:12:50)
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: The food dispenser in the drive room is now in the place that the door to the Captain's office was in the previous episodes. (00:16:15)
Revealing mistake: The cigarette butts that Lister supposedly tips out of his lager can were obviously in between his hand and the can, and not in the can at all. (00:19:25)
Continuity mistake: When Lister is revising for the exam, he opens a can of beer which sprays foam onto the table, and onto his cigarettes, when he opens it. A few seconds later, the sprayed foam disappears from the table. (00:19:30)
Continuity mistake: When Rimmer is talking to Lister before the exam and says they are friends, Lister replies "When?" Lister has a can of beer on the bunk, with the label facing the camera. Two shots after, the label is suddenly facing away from the camera. A couple of shots after that, the label is suddenly facing the camera again. (00:23:15)
Revealing mistake: When Lister leaves for his exam, he walks through Rimmer. As he does, both Rimmer and Lister become transparent when it should have just been Rimmer. (00:25:50)
Continuity mistake: Lister's rolling pin is dirty with flour when Christine walks in, but when Lister turns around, it's clean. Then it's dirty two seconds later, and then disappears completely after Lister drops the bowl. (00:26:12)
Continuity mistake: When Lister first sees Kochanski his locks are on top of his left shoulder. In the next shot they are gone, then back again when he drops the bowl. (00:26:15)
Continuity mistake: During Lister's exam, he takes the dough and puts it into the bowl while talking to Kochanski. When she turns into Rimmer, Lister is still rolling the dough and it is not in the bowl. (00:27:00 - 00:28:25)
Visible crew/equipment: When Lister is speaking to Kochanski and realises it is actually Rimmer, Kochanski says "it's Kochanski's body, it's Kochanski's voice" and a red boom mic is visible at the top of the screen. (00:27:45)
Continuity mistake: After Rimmer walks out of Lister's exam at The End of the episode, you can see he walks into the sleeping quarters, yet in the next shot he is walking down a corridor. (00:28:30)
Visible crew/equipment: When talkie Toaster says, 'I toast, therefore I am.', you can see the legs of a crew member moving in the reflection of the toaster. (00:04:40 - 00:11:50)
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)
Continuity mistake: After Rimmer and Lister argue about the pod, Rimmer walks off and Lister steps into the observation room. As Lister steps in, his locks are over his left shoulder, then in the next shot they are over his right shoulder. (00:14:05)
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 Rimmer wakes Lister up, as he stands up you can see he moves Lister's duvet with his shoulder, which he can't do, being a hologram. (00:15:20)
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