I happen to have this handy, since my next story riffs off this very conversation. *bg*

(Completely straight-faced conversation while going up the stairs to the teacher's apartment in Victory for Humanity.)

Danny: This is three, just two more to go.

Martin: Why is it that no one in a walk-up ever lives on the first two floors?

D: Vampires.

M: Really?

D: They have all the lower apartments all to themselves.

M: No direct sunlight, right?

D: Exactly. Plus they live to be a hundred and sixty years old, so the apartments never turn over.

M: That's good to know.