You kinda have to, round here. [Get used to all sorts of magic things.] Huh, I see. So your element's the one that's weak against fire. So it sure as hell ain't water, and not earth if that's the one it's strong against. [He pauses, and:] Air? [That is Korra's fourth element, at least.]
Well, if it ain't a secret, why'd you try to pass it as one? [He sounds vaguely amused, though.]