Harry shot Hermione a worried look. "No," Hermione said quickly, "it’s not even taught at Hogwarts except to warn you about it. Magical Theory by Aldabert Waffling says, "Blood magic is potent beyond all other kinds, but its power is difficult to control. It seeks to bind things tightly together, and scorns attempts to direct its power elsewhere. Unless correctly used in a properly designed ritual, it will do as it will, and bugger all to your plans.’"