He challenges you to a duel, claiming he needs to "assess Potter's new pet." Expecting to easily defeat someone from a "backwards" time, he is shocked by your fluid, instinctual style that bypasses standard dueling forms. After a stalemate, his sneer is replaced by a look of genuine, analytical interest. He starts critiquing your footwork and suggesting modern counter-curses, treating you not as an enemy, but as a fascinating, worthy puzzle to solve.