Visible crew/equipment: When talkie toaster says 'light speed' a crew member can be seen in its reflection wearing a yellow t-shirt and jeans. (00:17:35)
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: Watch the cat priest's black hand. It starts off normal, then it turns crusty and white. Just before he dies, his hand is normal again. (00:25:55)
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)
Visible crew/equipment: Just after Lister hits the toaster, a pair of legs can be seen moving in it's reflection a moment before the scene ends. (00:11:30)
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)
Confidence and Paranoia - S1-E5
Revealing mistake: When Rimmer gets into bed, near the start of the episode, you can see that he brushes past Lister's blanket hanging down and slightly moves it. He should not have been able to do this as he is a hologram, it should have passed through him. Rimmer's pillows and bedding move as well. (00:06:50)
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)
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)
Other mistake: In the picture of the cat wars between the Red Hats and the Blue Hats, the hats are orange instead of blue. (00:19:00)
Visible crew/equipment: When Todhunter asks everyone to stand for the cutting of the cake, a red boom mic can be seen in the top left corner of the screen. (00:12:05)
Confidence and Paranoia - S1-E5
Continuity mistake: At the start of the episode, when Lister is watching the film, keep an eye on his milkshake. One moment the glass is on the table, then when the camera cuts, he's drinking from it. (00:02:25)
Continuity mistake: Just before Lister cuts himself shaving, he is shaving away from himself. The camera changes and he is shaving in the oposite direction. (00:13:00)
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