Chapter 25, Fred and George talking about the Marauder's Map, which is supposed to show all people in Hogwarts by name:
“Still on the fritz,” said George.
“Both, or—”
“Intermittent one fixed itself again. Other one’s same as ever.”
The intermittent one is probably Quirrell, going in and out of zombie mode. But what could be visibly wrong with the other one? My theory is that, unlike all the other dots on the Marauder's Map, one of them doesn't have a name. Who could that be?
I hypothesize that this is Mr. Hat and Cloak. That would mean it's not Quirrell and not anyone the Weasleys would pay much attention to, either. The map must get the names it displays from somewhere, and its reliability in doing so suggests that it gets them from people's minds. My hypothesis is that to appear on the map without a name, you'd have to (a) not be known by name and present appearance to anyone whose mind the map can read, and (b) be an occlumens.
My guess is, the intermittent one is H&C taking the appearance (and name, on the map) of students who are elsewhere to walk among the children, listening to rumours, maybe even talking to them. I'm going to assume he can disappear as well as change shape when out of sight, otherwise it would be too easy to track him down; plus, that's why it's 'intermittent'.
(The HPMOR discussion thread after this one is here.)
This is a new thread to discuss Eliezer Yudkowsky's Harry Potter and the Methods of Rationality and anything related to it. There haven't been any chapters recently, but it looks like there are a bunch in the pipeline and the old thread is nearing 700 comments. The latest chapter as of 7th March 2012 is Ch. 77.
There is now 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.
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, nine.
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: