Severus glanced up at her as he was pushing the notebook aside; he waved at the chair on the opposite side of his desk, a silent invitation to sit. "The essential ingredient in various memory aides and the occasional sedative - highly toxic, and available on the southern bank of the lake in some quantity, if you ever need it." And a symbol of happiness remembered or returned - he couldn't recall which - in some of the more foolish spiritual traditions. "Which I don't expect you shall, in your line of work, unless you want to make your class particularly drowsy." Not a bad idea. He paused. "You don't need my permission to settle with your own House ghost, you know."