Harry Potter and the Methods of Rationality

The parchment vanished, and was replaced by another so quickly it was like the material had only flickered.

Then the lips moved as well. "And from this," whispered the lips, "you infer what, Mr. Potter?"

Harry was shaken by the sight, but his voice stayed even as he said, "That ordinary people do not always do nothing, and that Hermione Granger is in more danger from Slytherin House than you thought."

The lips curved, ever so barely. "So you think I have failed in my grasp of human nature. But that is hardly the only possibility, boy. Do you see the other?"

Harry furrowed his brows as he stared at the Defense Professor.

"I tire of this," the Defense Professor whispered. "You will stand there until you see it for yourself, or else leave." As though Harry had stopped existing, the Defense Professor's eyes looked back to the parchment, once more scanning back and forth.

It was six parchments later that Harry saw it, and said out loud, "You think your prediction failed because there was some other factor at work which was not in your model. Some reason why Slytherin House hates Hermione more than you realized. Like when the orbital calculations for Uranus were wrong, and the problem wasn't in Newton's Laws, it was that they didn't know about Neptune -"

The parchment vanished, and was not replaced. The head rose from its lolling position then, facing Harry more directly, and the voice which issued forth was quiet, but not toneless. "I think, boy," Professor Quirrell said softly, but in something approaching his normal voice, "that if all Slytherin House hated her so much, I would have seen it. And yet three formidable fighters of that House did something rather than nothing, at risk and at cost to themselves. What force could have moved them, or willed their motion?" The icy blue glitter of the Defense Professor's eyes met Harry's own gaze. "Some hand possessed of influence within Slytherin, perhaps. Then how would that hand have benefited itself by harm done to the girl and her followers?"

"Um..." said Harry. "It would have to be someone threatened by Hermione somehow, or someone who would get the credit if she was hurt? I don't know anyone who fits that profile, but then I don't know much about anyone in Slytherin outside first-year." The thought was also coming to Harry that deducing a hidden mastermind from a single mildly-unexpected attack seemed like insufficient evidence to support the prior improbability of the theory; but then it was Professor Quirrell who was doing the deducing...

The Defense Professor was just looking at Harry, eyelids slightly lowered as though in impatience.

"And yes," said Harry, "I am sure that Draco Malfoy isn't behind it."

A hiss of outward air like a sigh. "He is the son of Lucius Malfoy, trained to the most exacting standards. Whatever you have seen of him, even in what seem to be unguarded moments when his mask slips and you trust that you have seen the truth beneath, even that may all be part of the face he chooses to show you."

Only if Draco successfully cast the Patronus Charm as part of keeping up the act. But Harry didn't say that, of course; instead he just grinned slightly, and said, "So either you've really never read Draco's mind, or that's just what you want me to think."

There was a pause. One of the hands turned over, beckoned a finger.

Harry stepped into the room. The door closed behind him.

"That was not something you should have said aloud in human speech," said Professor Quirrell's soft voice. "Legilimency, on Malfoy's heir? Did Lucius Malfoy learn of it, he would have me assassinated outright."

"He would try," Harry said. It should have won a crinkle of Professor Quirrell's eyes, but the Defense Professor's face was unmoving. "But sorry."

When the Defense Professor spoke again, his voice had once more become a cold whisper. "I suppose I could, and pity the assassin." His head fell back against the chair, lolled to one side, the eyes no longer meeting Harry's. "But these small games hardly hold my interest as they stand. Add Legilimency, and it ceases to be a game at all."

Harry hardly knew what to say. He'd seen Professor Quirrell in an angry mood once or twice before, but this seemed emptier, and Harry didn't know what to say to it. What's bothering you, Professor Quirrell? he could not ask.

"What does hold your interest?" Harry said a few moments later, after he'd worked it out as a safer-seeming strategy for redirecting Professor Quirrell's attention to positive things. Citing experimental results about keeping a gratitude journal as a strategy for improving life happiness didn't seem like it would be taken well.