My personal guess about it is that it is that most people attribute to animals a lot more agency than they really have, and the story is written with an authorial worldview that assumes that most people's views on this matter are actually true. Given that worldview, no explanation is needed at all. Of course, that worldview is itself inconsistent, but the inconsistencies have relatively little relevance to talking to snakes.
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 113.
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.)
IMPORTANT -- From the end of chapter 113: