Narcissa pursed her lips. "Same goes for people. If you wouldn't know about the heritage of Crabbe and Goyle, you would never have thought they are purebloods. And as far as I'm aware, there's a really smart and extremely powerful muggle born witch in your year at Hogwarts. If you wouldn't know about her heritage, you would have begged your father to visit her parents and get the papers done, so she would be yours someday."