[The fact that Skulduggery feels the need to repeat the same sentence, combined with the 'planet' and the increased incredulity in his tone the second time, tells Kratos exactly what that sentence is. The repeat of that word 'you' suggests that's the part which refers to him.]

You're. Ah.

[Kratos goes back to the letters, seeking out one which corresponds to those sounds. The book, it proves, also has words for the passing of time, hours to years, day and night, and seasons. These are not immediately helpful.

[Next he consults the other two books in conjunction. He finds 'you', but doesn't understand the explanation; that's alright. He finds it in the thinner book, and this does have pictures. 'You' leads him to 'I' leads him to 'be' leads him to 'am' leads him into an increasingly deep circle of vocabulary with all his dogged intensity.

[By the time the car pulls up, Kratos is using the second picture book to sound out some basic sentences, and only stops to look up when Skulduggery turns off the engine.]