With a slight frown, Katara studied his back for a moment. She had noticed the sagging of his shoulders and that, strangely enough, bothered her more than anything else about his behavior thus far. She took a few steps closer.
"Zuko..." She stopped. What was she supposed to say? He wasn't Sokka. She couldn't demand an answer from him and expect him to just cooperate like her brother usually did. She also couldn't reason with him like she could Aang. Or rile him up enough to get a reply like with Toph. She knew Zuko well enough, she supposed, but she didn't know him well enough to provoke a conversation about something he clearly didn't want to talk about.
With a sigh, she tried again.
"How is Aang's training going?" There. That was a neutral enough topic for them, right? And one she had a right to ask, both as Aang's friend, as well as a fellow Master Bender who was also training the Avatar. Granted, Aang was training in order to kill Zuko's father, but surely Zuko didn't have a problem with that. If he did, he would never have agreed to train him in the first place. Right?