Lister is trying to teach Kryten to lie, and Kryten says he can't, because he is programmed to always tell the truth. However, in "The Last Day", he just lied to Hudzen about there being no Silicon Heaven.
Kryten initially tells Camille that he is unable to lie because he is a mechanoid, so that he won't upset her, but then he later tells Camille in the cinema that he watched "Casablanca" earlier with Lister to teach him how to lie, yet he continues lying until she leaves with Hector.
While teaching Kryten to lie, Lister mentions (Lord) Nelson putting a telescope to his blind eye and stating he didn't see any ships. At the Battle of Copenhagen, Lord Nelson did put a telescope to his blind eye but stated he saw no signals (not ships). The signals were for him to withdraw his ships. By ignoring the signal, Nelson went on to win the battle. Lister saying (incorrectly) ships instead of signals, was probably deliberate to emphasis Lister's limited education.
Kryten tells Camille that he would compute a 3 million digit prime number with prime roots for her. But a prime number has, by definition, no roots other than itself and one.