“If Only We Knew”
Sokka: See the problem with the old war balloon was you could get it airborne, but once you did, it just kept going. (He demonstrates with a model that goes up and hits the ceiling.) You could put a hole in the top, but then all the hot air would escape. So the question became, how do you keep a lid on hot air?
Katara: Ugh, if only we knew.