Continuity mistake: When Howard and Crawford are transported to Trojan, two of the three teleporter doors are open. When Crawford goes through the teleporter, one of the three doors close. Yet when Cat puts the resentment file into Crawford's neck, she starts shooting at everything including the teleporters, and now all the doors are open. (00:23:00 - 00:26:30)
Continuity mistake: When Lister notices the video, the silhouette of a flashing blue light is cast on the table (to the left of screen). In the next shot, there is no sign of the flashing blue light. (00:10:40)
Continuity mistake: When the book "Roots of Coincidence" is first seen it's a paperback but later in the episode it's suddenly a hardback.
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