(The HPMOR discussion thread after this one is here.)
The previous thread is over the 500-comment threshold, so let's start a new Harry Potter and the Methods of Rationality discussion thread. This is the place to discuss Eliezer Yudkowsky's Harry Potter fanfic and anything related to it. The latest chapter as of 09/09/2011 is Ch. 77.
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, seven, eight. The fanfiction.net author page is the central location for information about updates and links to HPMOR-related goodies, 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:
You do not need to rot13 anything about HP:MoR or the original Harry Potter series unless you are posting insider information from Eliezer Yudkowsky which is not supposed to be publicly available (which includes public statements by Eliezer that have been retracted).
If there is evidence for X in MOR and/or canon then it's fine to post about X without rot13, even if you also have heard privately from Eliezer that X is true. But you should not post that "Eliezer said X is true" unless you use rot13.
Re Chp 35
I searched all the threads, and didn't find any mention of this. There's a hint in the conversation between Hat&Cloak and Zabini: namely, the fact that there is a conversation at all. Why does H&C need to talk to Zabini if he's just going to obliviate him anyway? Here's one possible answer: he needs some information from Zabini.
I don't think he needs Zabini's report on the conversation — partly because he keeps talking afterwards, and partly because there are independent reasons to think that H&C is either Quirrel or an agent of Quirrel's. (For instance, the "keyed into the wards" comment, as well as the fact that H&C exactly predicts Quirrel's reaction to Zabini's statement, and the fact that this statement ended up benefiting Quirrel.)
So what information does H&C need? Note that he tells Zabini, "The reward I promised you is already on its way to your mother, by owl." In other words, Zabini was clever enough to insist that his reward go to a third party, leaving someone around to remember that he's owed an award in case he's obliviated. H&C seems to me to be turning the conversation at every step towards Zabini's mother. Eventually, he receives the information that Zabini doesn't know how his mother persuaded her last suitor to marry her.
It's unclear why this information would satisfy H&C, but it does seem that he needs to take care of Zabini's mother in some way (obliviate her, probably), and that he's trying to figure out how difficult this will be. This seems reminiscent of Quirrel's later behavior towards Auror Bahry — he tries to figure out exactly what Bahry knows and what the other aurors expect so that he can appropriately memory-charm him.
Any thoughts on the matter?
I think you might be overthinking things. H&C keeps bringing the conversation around to the consequences of serial betrayal. One off-hand remark (the "keyed into the wards" comment) leads Zabini to think about his guesses as to who H&C might be. The Obliviation only comes after Zabini thinks to himself that no one gave him a chance to sell out H&C.