Revealing mistake: Just after the Trojans' conversation, there are two jolts. Lister jumps back too soon on the second jolt. (00:03:30)
Quarantine - S5-E4
Revealing mistake: As pointed out by Danny John Jules on the DVD Commentary, during the 'Feckles, Heckles, Hackles, Schmeckles' argument, Cat pushes his face right against Kryten's, leaving a brown makeup smear on Kryten's forehead. The mark is gone in the next shot. (00:19:45)
Revealing mistake: The low Cat's teeth move and wobble in ways they should not be able to when he is first seen. (00:14:10)
Revealing mistake: The pyrotechnic charges are visible under the 'High' Cat and Kryten's robes, before they are shot. There is also a wire trailing behind Kryten and running up his left leg, presumably a means of detonating the charges. (00:12:45)
Revealing mistake: When Lister slams his nose into the door of the cabinet, you can see it is nowhere near it. (00:17:50)
Terrorform - S5-E3
Revealing mistake: At the start of the episode, Kryten's real wrist can be seen just before he removes his hand. (00:02:30)
Revealing mistake: After Starbug lands on the 'high' Red Dwarf, Rimmer is running out of power and starts to fade in and out. However, Cat, who must be standing too close to Rimmer also fades, the backdrop being partially visible through him. (00:08:05)
Revealing mistake: At the very start of the episode, when the SSS Esperanto is seen, the bubbles from the seabed are sinking rather than rising, revealing the piece of footage is being played backwards. (00:00:35)
Quarantine - S5-E4
Revealing mistake: When Lister uses the keypad to escape from Quarantine, more button lights turn off than he has actually pressed. (00:23:35)
Quarantine - S5-E4
Revealing mistake: When Lanstrom corners Lister, Kryten and the Cat, she is holding onto the fence. As she is a hologram, this would be impossible. (00:10:10)
Revealing mistake: During the car chase, the box Rimmer is sitting on keeps moving. (00:21:25)
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 ★