"The Dark Lord came to Godric's Hollow," said McGonagall in a whisper. "You should have been hidden, but you were betrayed. The Dark Lord killed James, and he killed Lily, and he came in the end to you, to your crib. He cast the Killing Curse at you. And that was where it ended. The Killing Curse is formed of pure hate, and strikes directly at the soul, severing it from the body. It cannot be blocked. The only defense is not to be there. But you survived. You are the only person ever to survive. The Killing Curse reflected and rebounded and struck the Dark Lord, leaving only the burnt hulk of his body and a scar on your forehead. That was the end of the terror, and we were free. That, Harry Potter, is why people want to see the scar on your forehead, and why they want to shake your hand."
Saying that a spell severs the soul from the body comes along with the strong implication of not killing someone via bodily harm.
He hasn't heard the incantation yet, that's true. But he just heard plenty about the Killing Curse.
edit: I'm fairly confident that the concept of magic forensics is not beyond him at the moment.
Besides, looking at it narratively, there has been way too long of a wait to find out what that meant for the payoff to be minor.
He just heard plenty about the Killing Curse, yes. But that plenty doesn't include anything about what people who have been struck by it look like. I am not even slightly convinced that "it severs the soul from the body" carries a clear implication that it doesn't damage the body in the process. (Contrast "it removes the brain from the skull". If you heard that someone had had his brain removed, would you then be surprised if his head looked a mess?)
Update: Discussion has moved on to a new thread.
The load more comments links are getting annoying (at least if you're not logged in), so it's time for a new Harry Potter and the Methods of Rationality discussion thread. We're also approaching the traditional 500-comment mark, but I think that hidden comments provide more appropriate joints to carve these threads at. So as of chapter 67, this is the place to share your thoughts about Eliezer Yudkowsky's Harry Potter fanfic.
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: one, two, three, four, five, six. The fanfiction.net author page is the central author-controlled HPMOR clearinghouse with links to the RSS feed, pdf version, TV Tropes pages, fan art, and more, and AdeleneDawner has kept an archive of Author's Notes.
As a reminder, it's often useful to start your comment by indicating which chapter you are commenting on.
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: