Remus Lupin doesn't know what to do. He could pretend he's just an ordinary boy - that the full moon hasn't sentenced him to a life of misery and secrecy, pain and insanity. He could, momentarily, metaphorically, drain all the werewolf blood from his veins. He could purge his mind of what he cannot purge his body. He's only eleven, after all. He's young enough, and new enough, to remember a time when he was perfectly normal. When he transforms, the wolf is still weak, and the moonlight still somewhat beautiful.
But he is too stubborn a realist to deceive himself, too horrified. Too ashamed.
When the Sorting Hat shrieks "GRYFFINDOR!" he loses all sense of time and place, until Sirius's whoop of triumph, louder somehow than all the rest of the noise in the Great Hall combined, reminds him to get off the stool. Then he smiles, faintly, self-consciously.
He'd been sure it would be Slytherin.
Perhaps for one dark moment, he had wanted it to be.