Ah! If that's true, then Quirrel's explanation is a lot more convincing... in fact, I think that tips me well over the edge of uncertainty into believing Quirrel's account is correct.
Thanks! (As may be obvious, I'm not actually that much of an HP fan. I've read a few of the books and have some grasp of the world, and have browsed some online sources while thinking about the various puzzles in MOR, but I'm woefully ignorant. In fact, I got through most of MOR before realizing that Quirrel had been Quirrelmorted in the original.)
This is probably a place where Q's original lesson on the curse in MOR (the one where he keeps saying, "One killing curse will bring it down!") might have been usefully supplemented by it being mentioned that it's the only unblockable spell -- as opposed to just saying that nobody can block it.
However, there's plenty of places in MOR where shock and awe are expressed over Harry's surviving a (presumed) direct hit from the killing curse. IOW, it's shown in MOR that the killing curse is unblockable and that this is an important fact about it. But perhaps for this particular plot point, it isn't emphasized enough that it's the only fighting spell that can't be blocked by something.
- This thread has run its course. You will find newer threads in the discussion section.
Another discussion thread - the fourth - has reached the (arbitrary?) 500 comments threshold, so it's time for a new thread for Eliezer Yudkowsky's widely-praised Harry Potter fanfic.
Most of the paratext and fan-made resources are listed on Mr. LessWrong's author page. There is also AdeleneDawner's collection of most of the previously-published Author's Notes.
Older threads: one, two, three, four. By tag.
Newer threads are in the Discussion section, starting from Part 6.
Spoiler policy as suggested by Unnamed and approved by Eliezer, me, and at least three other upmodders:
It would also be quite sensible and welcome to continue the practice of declaring at the top of your post which chapters you are about to discuss, especially for newly-published ones, so that people who haven't yet seen them can stop reading in time.