"S-Studying with ones peers is not the same as teaching, Doctor. When I studied..." He trailed off suddenly with a look of dawning horror, as if he'd only just realized those memories of his childhood--indeed everything before some point at Farringham--never, in fact, happened. They were in his memories and felt as real as everything he remembered with Joan, and yet his school, his friends and his family were simply phantoms of his imagination. Just stories.
For a long few moments, he could only stare at the Doctor, freshly horrified. What was one to say to the realization that they'd never tasted their favorite food, and the mother who did their wounds never even existed in the first place. In a way he'd already known it with the knowledge that the Doctor created him, but there had been a certain level of denial left in him that some portion of his memories to that point were real.