Perhaps it was because, although they were excited, they had not yet been loud enough for her to find them unbearable.
Ron's fingers curled and uncurled unconsciously on the tabletop, then curled again. His lips moved as though he were muttering something soundlessly. When Hermione said the word "instinct," his face turned awful, as though someone were using his stomach as a blender.
"But—if spiders really did it, why wasn't anyone wrapped in webs and eaten? The petrified students were only petrified. They weren't dragged away, they weren't—they weren't eaten. Spiders wouldn't leave meat sitting right in front of them."
Hermione's fingers tapped lightly against the table, once after another. The sound was quiet but steady, like a patient clock that would never hurry.
"Because every attack was discovered quickly. When Colin was found, the screams spread almost immediately. When Justin and Nearly Headless Nick were found, there were people in the corridor. When Fuli Dolun was attacked, his companions were right beside him and called the professors. Spiders are extremely cautious creatures. No matter how much their size changes, their instincts do not. They would not stay behind to eat while humans were gathering around their prey."
"And there's also a herd of Centaurs in the Forbidden Forest." Hermione's fingers stopped on the tabletop, as if she had finally placed the last puzzle piece into its empty space. "Centaurs hate Acromantulas. They regard spiders as things as dangerous as Dark wizards. The moment they see spiders crossing their territorial boundary, they attack. Not to protect humans, but to protect their own territory. Yet the result is the same—the spiders are driven back."
Ron's fingers curled unconsciously on the table, uncurled, then curled again. "Centaurs... Thestrals... professors regularly clearing them out with upper-year students... Hagrid keeping watch... and Aragog himself