The other rooms were trapped, but Quirrel detected and disarmed the wards. In Snape's room, he detected no wards, and that's what makes him suspicious.
Snape has much better muggle lore than the average wizard. I'm guessing anyone trying to solve that room with violence will get a faceful of claymore mine or the equivalent. No wards detectable because the traps are not magic.
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: