Continuity mistake: When Ace drives the bike out of the shed, the piece of wood is between the front wheel and the handlebars. In the next shot, the piece of wood is resting on his arms. (00:03:25)
Revealing mistake: When Kryten's head explodes, you can tell the head is a dummy. (00:08:05)
Continuity mistake: When the gunman ties the cable to himself, he walks past a window, then in the next shot he is stood in the centre of the same window. (00:15:40)
Revealing mistake: When Kochanski is on the phone falling through space, her lips do not match what she is saying. (00:25:55)
Continuity mistake: When Kochanski is in bed at the start of the episode, she is wearing stud ear rings. When she gets up to go to the kitchen area, they are now hoops. (00:02:20 - 00:03:50)
Continuity mistake: When Able takes his head off and throws it at the simulant, he throws it forwards towards where Lister is standing. The head manages instead, somehow, to hit the simulant standing next to the gelf on Able's left. (00:20:00)
Revealing mistake: When Lister kicks the simulant in the head, you can see he misses him by about a foot. (00:20:00)
Continuity mistake: The cable attached to the gunman is pulled away from the wall when he shuffles past the window, yet when Lister opens the window, it is still attached. (00:15:55)
Continuity mistake: At the start of the episode when the Nazi commander is speaking to Ace, in all wide shots his left arm is wrapped around the crocodile, but in all close up shots his arm is by his side. (00:00:45)
Plot hole: The alligator that falls out of the plane with Ace hits the ground several minutes after Ace does. (00:04:25)
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