The cold in the room seemed to deepen. "A sixth-year Gryffindor cast a curse at one of my more promising students, a sixth-year Slytherin."

Harry swallowed. "What... sort of curse?"

And the fury on Professor Quirrell's face was no longer contained. "Why bother to ask an unimportant question like that, Mr. Potter? Our friend the sixth-year Gryffindor did not think it was important!"

"Are you serious? " Harry said before he could stop himself.

"No, I'm in a terrible mood today for no particular reason. Yes I'm serious, you fool! He didn't know. He actually didn't know. I didn't believe it until the Aurors confirmed it under Veritaserum. He is in his sixth year at Hogwarts and he cast a high-level Dark curse without knowing what it did."

"You don't mean," Harry said, "that he was mistaken about what it did, that he somehow read the wrong spell description -"

"All he knew was that it was meant to be directed at an enemy. He knew that was all he knew."

— Harry Potter and the Methods of Rationality by Eliezer Yudkowsky