Harry Potter and the Methods of Rationality

Lavender were all gone for the holidays, but at least that left...

"What was all that ruckus at the Head Table?" Harry said to the Weasley-twin group-mind, as he began to serve himself his own plate. "It looked like it was just ending as I walked in."

"Our beloved, but clumsy Professor Trelawney -"

"Seems to have gone and dropped an entire soup tureen on herself -"

"Not to mention Mr. Hagrid."

A quick glance at the Head Table confirmed that the Divination Professor was waving her wand frantically as the half-Giant dabbed at his clothes. Nobody else seemed to be paying much attention, even Professor McGonagall. Professor Flitwick was standing on his chair as usual, the Headmaster seemed to be absent again (he'd been gone most days of the holiday), Professors Sprout and Sinistra and Vector were eating in their usual grouping, and -

"You know," Harry said, as he turned his head away to stare at the ceiling illusion of a clear blue sky, "that still creeps me out sometimes."

"What does?" said Fred or George.

The powerful and enigmatic Defense Professor was 'resting' or whatever-the-heck-was-wrong-with-him, his hands making fumbling, hesitant grabs at a chicken-leg that seemed to be eluding him on the plate.

"Eh, nothing," said Harry. "I'm not quite used to Hogwarts, yet."

Harry continued to eat in moderate silence, as various Weasleys discussed some bizarre mind-affecting substance called Chudley Cannons.

"What sort of deep mysterious thoughts are you thinking?" said a young-looking witch with short hair, sitting nearby. "I mean, just curious. I'm Brienne, by the way." She was gazing at him with one of those looks which Harry had firmly decided to just ignore until he was older.

"So," Harry said, "you know those really simple Artificial Intelligence programs like ELIZA that are programmed to use words in syntactic English sentences only they don't contain any understanding of what the words mean?"

"Of course," the witch said. "I have a dozen of them in my trunk."

"Well, I'm pretty sure my understanding of girls is somewhere around that level."

A sudden hush fell.

It took a few seconds for Harry to realize that, no, the entire Great Hall wasn't staring at him, and then Harry twisted his head around to look.

The figure who'd just staggered into the Great Hall appeared to be Mr. Filch, Hogwarts's token hallway monitor; who, along with his predatory cat Mrs. Norris, constituted a low-level random encounter whom Harry often breezed past wearing his epic-level Deathly Hallow. (Harry had once consulted the Weasley twins about pulling some sort of prank on this deserving target, whereupon Fred or George had quietly pointed out that Mr. Filch was never seen to use a wand, which was odd, really, considering how many spells would be useful in that position, and it made you wonder why Dumbledore had given the man a position at Hogwarts, and Harry had shut up.)

Right now Mr. Filch's brown clothing was disarrayed and soaked with sweat, his shoulders were visibly heaving as he breathed, and his everpresent cat was missing.

"Troll -" gasped Mr. Filch. "In the dungeons -"

Minerva McGonagall stood up from the Head Table so quickly that her chair fell to the ground behind her.

"Argus!" she cried. "What happened to you?"

Argus Filch staggered forward from the huge doors, his upper body streaked and dotted with small crimson dots as though someone had spattered steak sauce over his face. "Troll - grey - twice as tall as me - it - it -" Argus Filch covered his face with his hands. "It ate Mrs. Norris - ate her all up, in just one bite -"

Minerva felt a stab of dismay in her other self, she hadn't liked the other cat very much but the two of them had still been felines.

An uproar started from the Great Hall. Severus stood up from the Head Table, somehow doing so without drawing any visible attention to himself, and strode out the huge doors without another word.

Of course, Minerva thought, the third-floor corridor - this could be a distraction -

She mentally consigned all such matters to Severus's care, drew her wand, raised it high, and let out five sharp cracks of purple fire.

There was stunned silence but for Argus's broken sobs.

"It seems we have a dangerous creature loose in Hogwarts," she said to the faculty at the Head Table. "I will ask you all to aid in searching the halls." Then she turned to the stunned and watching students, and raised her voice. "Prefects - lead your houses back to the dormitories immediately!"

Percy Weasley leaped up from the Gryffindor table. "Follow me!" he said in a high voice. "Stick together, first- years! No, not you -" but by that time the other prefects were raising their own voices as a renewed babble sprang up.

Then a clear, cool voice spoke under the sudden rush of sound.

"Deputy Headmistress."

She turned.

The Defense Professor was calmly wiping off his hands on a napkin as he stood up from the Head Table. "With respect," said the man of unknown identity, "you are not expert in battle tactics, madam. In this situation, it would be wiser to -"

"I do apologize, Professor," said Professor McGonagall, as she turned toward the great doors. Filius and Pomona had already risen to follow her, with Rubeus Hagrid towering over all of them as the half-giant stood up.