Voldemort has an absolute truth oracle, or at least a sufficiently good approximation thereof, available too him. If Harry needs his wand to teach V one of his secrets, make him say so in Parseltongue. If H does demand his wand, make him state whether he intends to use it for anything but demonstrating a secret.
The wonderful thing here is that this gives all kinds of opportunities for V to screw up without realizing he's screwing up. PT is a secret for which H needs his wand. H is, in a sense, demonstrating PT. Unless V was very careful about making H state his exact and full intentions, we could have had a plausible reason for H to have his wand. There's really no plausible reason for V to just let him have it, though; disarming him (there's even a spell which does exactly that, and one would hope his followers know it...) costs nothing but a small amount of time, and gains V potential defense against "a power he knows not"... the existence of such things being the whole reason V didn't just have H killed immediately!
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 117.
Plans for next chapter release:
There is a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)