It's the same as with Hermione's body and the unicorns. They are stones as long as they are Transfigured. When Transfiguration stops, they will soon suffer. That's why Harry kept Hermione's body and now thinks about sustaining the Transfiguration of Voldemort all the time - he wants them to stay Transfigured until their state can be helped. He's kind of frozen now.
Ah, thanks.
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 114, and also, as a special case due to the exceptionally close posting times, chapter 115.
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.)