As he turns, his magic building up around the charm and the words spilling past his lips, he confirms why. You only feel auras of people stronger than you -- a metaphysical difference according to some theorists and a defence mechanism according to others -- or around your own strength. The magic bursts into the room, the same way the magic of the vow had spread like an inky pool over her skin, and as Prongs comes into a blinding, solid existence he steals her breath away.