Harry can just claim to have already used it that day for an innocuous purpose, like studying or something. Sure, McGonagall could accuse him of stupidity because that leaves him unprepared for an emergency, but pleading guilty to stupidity is easy. (Well, easier, anyway.)
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 116.
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.)