Fire
He had a natural attraction to fire at least that's why he he felt the urge to anger her, for a glimpse of that fire in her eyes. That at least is what he would tell any one if they asked why he decided untie the back of Katara's swim suit. Her she covered herself with the mostly fallen top, eyes narrowed dangerously, Zuko could see the inferno of rage dancing behind them, he took a nervous step back. For every step back he took though she took one forward, the last thought he had before he took of running from the livid water bending master was, "When you play with fire you get burned."