What's so "Armor-piercing" about the Armor Piercing Question? The parasites are infecting and killing humans, and WE"RE savage for trying to defend ourselves!? How does that make any sense?!

What happened to Sanae,the girl with glasses who first recognises the monster inside the school? She throws acid over it, then jumps out the window and is hustled off, clearly alive, but we never hear anything more...