Also, won't Quirrell die of transfiguration sickness if he drinks the blood of transfigured Rarity?
No, the unicorn will, but by the time Quirrell drinks it blood it won't be transfigured any more, so he will be fine.
From chapter 100:
the blood must come from a live unicorn and the unicorn must die in the drinking
Quirrell doesn't have a very large window in which to drink the blood.
More to the point, wouldn't particulate matter, other fluids, other bits of the unicorn pollute the blood as a result of the transfiguration? I could see the blood itself fixing that issue, but in the case of another fluid in a similar situation, I could see the drinker getting sick (if not to the degree that the animal did).
I may not be understanding how transfiguration sickness works exactly.
EDIT: formatting
New chapter!
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 102.
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.)
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: