"It was a dragon." Nathaniel wasn't there for the archdemon, but he saw what he saw. "Maybe there is something, between all the strange things we know, some commonality. Archdemon blood is different from darkspawn blood. Warden blood is different from human. When darkspawn and humans drink one anothers' blood, we become more similar to each other. Perhaps a dragon cannot be corrupted by normal means, and the darkspawn do something we do not yet understand. But the flesh of a dragon burns away the Blight. What do you suppose the blood of a dragon do, if mere touch purifies?"