Other mistake: Kryten places Rimmer's light bee on the floor, then begins the process of reinitialising him. As the process finishes and Rimmer looks at Lister (who looks away), the light bee, which should be hovering within his torso projecting his image, is still visible on the floor between his feet. (00:06:00)
Other mistake: When Legion stabs his left hand, everyone grabs and shakes their left hands - except Lister, who grabs and shakes his RIGHT hand. (00:22:40)
Factual error: While it is true that lithium carbonate can be used to treat depression and other psychiatric disorders, it cannot be administered in gaseous form. It is a very stable salt and only starts to form vapour at 1,310 degress Celcius. Spraying it about as a 'mood stabliser' at that temperature, as Kryten does, is going to kill everyone on the spot.
Lister: Get real, man. Most eunuchs have got more balls than you.
Trivia: It was rumored that Alfred Molina and Alan Rickman wanted the part of Rimmer. Lee Cornes also auditioned for this role (he later guest starred on the show), as did Hugh Laurie. Robert Bathurst, Norman Lovett and David Baddiel auditioned for the role of Lister.
Chosen answer: In-universe, after leaving Red Dwarf after his first appearance, Kryten managed to crash Lister's space-bike into an asteroid. Lister found his remains and decided to rebuild him, however, due to the high level of damage and Lister's questionable repair skills, he was unable to recreate Kryten exactly, leading to changes in appearance, personality and accent. In reality, the original actor wasn't available, coupled with presumably practical concerns about one-off makeup as opposed to makeup for a regular cast member, so some visual changes were made.
Tailkinker ★