That sounds reasonable, but unless everything we saw about Quirrel is lie, he is unable to cast animal Patronus, being cynical sociopathic rationalist with a homicidal tendencies.
There is some possibility that Quirrel have analyzed his conversation with Harry, words about "rejection of Death as a part of natural order" and picture of stars being able to keep Dementation away and re-discovered True Patronus (there is speculation about Quirrel being enemy of Death, so it at least plausible), but True Patronus couldn't look like a snake.
PS: Your argument partly applies to the Patronus of Lucius being a snake, though.
Probably the only two things the True Patronus can look like are humans and snakes. Possibly flying squirrels?
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 96. The previous thread is at almost 300 comments.
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. (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.)
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: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, .
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