A bit of adolescent humor.

By the time the Southern Tribesmen left to war and the oldest remaining example of masculine pride was her bright, fool of a brother, Katara already understood that grandmothers have the last say in every decision and this was simply the way of the world. From her grandmother she learned to deliver babies--both animal and human--and acquired from an early age that inevitable knowledge of how her body worked and what she could expect of it. It's hard to be squeamish about a little blood of one's own when one has birthed a live, kicking snow carribou in one's backyard.

However, growing up with closely one chauvanist boy (and knowing several others before they disappeared over the horizon), Katara was constantly forced to witness and deal with certain attitudes about that time of the month and whether or not her crying and her anger was a result of mood swings or merely a logical, reasonable side effect of being in absurd amounts of pain. Adolescence brought new reasons to fight with her older brother, and it took a long, long time before she finally convinced him that girls who were menstruating were not crazy or icky, that no girl wanted to ever be told she was crazy or icky, and that if Sokka wanted to live to have a girlfriend he'd never imply Katara was either of those ever again.

In matters of social interaction, Prince Zuko at recently seventeen was not so learned, or so lucky, as Sokka had been at fourteen. Through arguably no fault of his own, Zuko happened to be absent for those crucial years of his sister's young adulthood, and never picked up that particular lesson about how not to talk to girls.

When he noticed Katara using her waterbending to a rinse bloody rag after the rest of the laundry, his first response was to ask whose blood it was. Upon realizing the answer to his own question (because no one had been injured in days), Zuko gave a nervous effort toward verbal backpedalling while, in an attempt to break the awkwardness, simultaneously dispensing a few butchered proverbs about growing up, and ended with the gem:

"And you don't have to worry--I won't tell anyone."

Katara bended the last of the water out of the cloth, and set it in the sack by her feet. She turned to him and asked, "What did you say? I didn't quite hear you."

He replied a little louder, but still tried to be inconspicuous. It was futile: the entire group was within hearing distance anyway. "I just said that I won't tell anyone about, you know, that you're..."

Katara looked at him darkly from her place by the wash bowl.

"Oh no," moaned Sokka. "Here we go."

"What? What exactly did he say?" Aang wanted to know, at first too busy playing with Momo to notice the rising tension.

"Trust me, he has it coming," said Toph. All their eyes followed Katara's form rise until she was looming over the cross-legged Zuko, bag of laundry glued to her hip and her arms crossed at her chest like a road block.

"And what," she growled, "does it matter that you saw me cleaning a bloody wash cloth?"

"Nothing, I guess," Zuko replied slowly, like he was testing the water and had found it decidedly too cold for swimming.

"So why bring it up? Am I supposed to be embarrassed, because it happens to make you nervous? Should I be ashamed of it?" Her volume increased with each successive question.

"No, that's not what--"

"Do you expect me to stammer and blush and look away just because you saw me cleaning blood out of a few rags? My blood? Maybe I need to explain it to you--"

"Uh, that's not necessary Katara--"

"--Because apparently they don't teach royal little brats about it, and you're probably feeling confused now, and wondering what you said that was wrong--"

"I'm sorry," he tried, but she would hear none of it.

"Sorry? You're sorry?" Katara shouted, "What are you sorry about? You can't even handle the sight of blood you stupid, stupid--boy! Yeah, it's blood! Blood blood blood! It's happens! Grow up!"

She threw the sack of laundry at his face and marched out of the camp. Zuko set the bundle gingerly on the ground; it took all his pride not to immediately shake his hands clean of imaginary ick. Then he noticed everyone else.

"What!"

Katara's brother sighed and shook his head. The young Avatar shrugged.

"You totally deserved that, Stomps-A-Lot," Toph said. "And you can stop being nervous all the time, because now she'll never kiss you."