"You know," Harry started conversationally, "I have always wondered if you knew about what I can do, the "thing’ I coined it. It turns out you both do." He surveyed them, satisfaction gleaming in his eyes. He pointed at Petunia, "When I levitated the knives, you looked at me in horror, but there was recognition in your eyes." He turned away and smirked at Vernon, "And you. You told me to stop the "freakishness’ but you weren’t surprised. That shows you both knew about it beforehand."