"Drawn in a combination of powdered silver and belladonna," Ginny explains. "You’ll summon him into it by pressing your brands. He won’t be able to escape it – nothing with a single drop of demon blood can cross a barrier made out of those ingredients. Which is why Ron, Harry and I can’t get too close; we can’t risk getting trapped in it ourselves. But you’ll be fine. We’ll give you a knife of blessed iron, and then you can just stab him. It’ll be easy!" She beams at Hermione as though she truly believes that.