Zuko grasps the subtle dig, but he doesn't rise to it. "That-- I don't even think Father, or Azula-- can do that. It's not..." He shakes his head, and says, "Lightening, that's -- the pinnacle. It takes years of education... or a certain... ability."

Ability that Zuko bleeds for and Azula laughs over.

"Mastery can take years. I only know two Firebenders who can do something like that."