"To go into someone's head to 'mess with it' you need legilimency. An art that only the most accomplished of wizards and witches have ever mastered. It takes willpower and intelligence, so if I was you, I wouldn't aim for that. The Dark Lord himself is a master of it, of course." And so was Barty, but he saw no need to add that right away. Ideally, Draco would find out soon enough. "Occlumency is the act of protecting one's mind. Something for which you, oddly enough, seem to naturally have a knack."

He took a step closer, facing Draco. "I want you to try and keep me out of your mind, right now. Or I will drag up something you don't want me to know."