Update: This post has also been superseded - new comments belong in the latest thread.
The second thread has now also exceeded 500 comments, so after 42 chapters of MoR it's time for a new thread.
From the first thread:
Spoiler Warning: this thread contains unrot13'd spoilers for Harry Potter and the Methods of Rationality up to the current chapter and for the original Harry Potter series. Please continue to use rot13 for spoilers to other works of fiction, or if you have insider knowledge of future chapters of Harry Potter and the Methods of Rationality.
A suggestion: mention at the top of your comment which chapter you're commenting on, or what chapter you're up to, so that people can understand the context of your comment even after more chapters have been posted. This can also help people avoid reading spoilers for a new chapter before they realize that there is a new chapter.
I never really understood the claim that there's no defense against Avada Kedavra. Sure, there's no direct countercurse, but you can dodge it or levitate an object between yourself and the curse (Dumbledore levitated a statue in front of Harry to protect him from the curse in Book 5). Both of these responses can be trained to the point of instinct, and voila, you have a defense.
Wait, the fact that the second strategy works is inconsistent. If the Killing Curse can be blocked by inanimate objects, why is it that clothing doesn't block it?
I forget if this happens in the book, but in the movies the curse damages obects badly when it hits them. So clothing may just be too thin and weak to absorb it.