Visible crew/equipment: When the vending machine says it will destroy Rimmer, a boom mic can be seen at the top of the screen. (00:06:05)
Continuity mistake: Just before Rimmer and Lister drink the hooch, Lister's locks are behind his back, then one of the locks moves to in front of his left shoulder during a brief shot of Rimmer. (00:13:30)
Other mistake: When Rimmer tries to silence the vending machine, he covers up the input microphone with stickers instead of covering the speaker just above it. (00:05:05)
Revealing mistake: When the Cat, Lister and Kryten are walking and the Cat is complaining about rock, keep an eye on the background. They start walking just before a set of steps, then do a complete loop back to the steps for no reason. (00:06:15)
Continuity mistake: When Rimmer gives Hollister the directives to sign, he holds the clipboard in both hands. In the next shot his left hand is under the first page. (00:02:15)
Visible crew/equipment: When we first see Rimmer and Lister in the medi-bay, the camera crew can be seen in the reflection of the tv. A boom mic arm can also be seen moving. (00:16:55)
Visible crew/equipment: After Rimmer faints after getting drunk, a boom mic shadow can be seen on the bedsheets. (00:15:45)
Continuity mistake: When Hollister picks up the lemon drink, his left hand is by his side. In the next shot it is on his chest. (00:01:50)
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