Iirc, in canon, the Gaunt family (Voldemort's family) was the last living set of descendants of Salazar Slytherin, and they were very inbred by the time of the books, so it appears that JKR at least provided some workaround for this.
As for the reliability of Parseltongue, there's some precedent for it apparently serving as truth-enforcement. Chapter 49:
"I am not regisstered," hissed the snake. The dark pits of its eyes stared at Harry. "Animaguss musst be regisstered. Penalty is two yearss imprissonment. Will you keep my ssecret, boy? "
"Yess," hissed Harry. "Would never break promisse."
The snake seemed to hold still, as though in shock, and then began to sway again.
[...]
"You ssay nothing, to no one. Give no ssign of expectancy, none. Undersstand?"
Harry nodded.
"Ansswer in sspeech."
"Yess."
"Will do as I ssaid?"
"Yess."
Professor Quirrell is known for his aversion to unnecessarily redundant conversation, so it seems likely here that he wants to be sure Harry is telling the truth. Later, in Chapter 66:
"Lessson I learned is not to try plotss that would make girl-child friend think I am evil or boy-child friend think I am sstupid," Harry snapped back. He'd been planning a more temporizing response than that, but somehow the words had just slipped out.
It would have helped Quirrell convince Harry in Azkaban, but it's possible he thought it would be more useful for Harry not to know yet how much information his unwittingly-true answers were giving Quirrell.
And might possibly have prompted Harry to insist on hearing about Bellatrix in Parselmouth.
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: