"You remember when we went in that house and there was nobody there, even though there were people there? That's a barrier," he explains. "People and magic inside it can't see or touch people and magic outside it or vice versa, but stuff like houses and tables is still in both. If there was a way to put a kind of - one-way barrier around a search spell, then most people wouldn't see it running around. I guess anybody who's good with barriers could still tell."