Your notebook! Beautiful thing, that. You've been here a while — longer than me, in any case — long enough you have a notebook and you're sat there observing and reading it, perhaps adding to it later.

[ It's not lost on the Doctor that the other man seems protective of said notebook. If anyone could possibly understand attachments (for reasons many and varied) to inanimate objects, it's this one. ]

I like thinkers and readers and notebook-keepers. Big fan myself! What were you thinking about?

[ Yes, he'll just launch right into it without any preamble. They've had a decent enough introduction, in the Doctor's estimation. Enough that he can absolutely ask such a question. ]