Another possibility is that snakes can't lie (lying depends on some brain feature they lack) and Parselmouthing people can't lie (part of how it works) but a snake animagus is neither and so can lie.
FWIW, I'm pretty sure that EY would endorse the claim that lying depends on a brain feature that snakes lack. Lying in the sense of deliberate deception requires a theory of mind of the one being deceived, and snakes aren't that intelligent, or so I believe that EY believes (and for that matter believe myself).
OTOH, snakes aren't intelligent enough to talk either; in HPMOR, they only do so by borrowing the mind of the Parseltonguer. And Parseltonguers can conceive of other minds, both for the benefit of snakes and for their own speech. So this doesn't prove anything.
Two new short chapters! Since the next one is coming tomorrow and we know it'll be short, let's use one thread for both.
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 105 (and chapter 106, once it comes out tomorrow). EDIT: based on Alsadius' comment about thread creation for MOR chapters, let's also use this thread for chapter 107 (and future chapters until this nears 500 comments) unless someone objects to doing so. Given that this is the final arc we're talking about, thread titles should be updated to indicate chapters covered.
There is 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. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
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: