The denizens of Winterfell learned a few things rather quickly.
Firstly, one did not anger Arya Stark lightly. At times it seemed difficult to say anything that wouldn't set her off, but there were a few things that were always treacherous ground – one didn't call her a lady, one didn't tell her not to do something (not to mention the part where she invariably did it anyway, because you'd told her not to) and one generally avoided bringing up the words "shouldn't you be…" whenever she invariably turned up in the stables looking furtive.
Of course, there were new rules all the time, and always exceptions, but generally if one was careful one didn't have to worry about running into any trouble.
"He's writing to Lady Sansa."
Of course, they also learned that even when it seemed no one was listening, it paid to talk quietly. Arya knew everything about the Winterfell grounds. Everything.
It never stopped the younger boys, though.
"Lady Sansa? Why? Don't be stupid…"
"She's pretty," someone muttered, sullenly. There was a roar of laughter.
"Yeah, but she's a Lady. Highborn."
"And she's a stuck-up little bitch besides," someone snorted, one of the older boys. "Thinks a lot of herself-"
It happened a bit too fast for anyone to really see what happened, but one moment the unfortunate boy was standing and the next he was on the ground holding his nose, which was dripping gobbets of blood to the hay. Arya Stark stood over him, small and sticklike and defiant.
"Want to say that again?" She demanded. Most of the boys backed off. The poor unfortunate tried to sit up.
"What's it to you?" He asked, belligerently. "I'll say what I want to-"
Arya kicked him in the ribs and said, eyes flaring, "She's my sister," before she turned and stalked away. Fearful that she was still watching, no one moved to help the injured boy to his feet.
*
It was later that Sansa found her sister nursing bruised knuckles in a quiet corridor. "Arya, what were you doing?" She asked, appalled. Arya looked up at her coolly, and seemed to be thinking. Then she shrugged.
"Fighting."
"Who?"
"Boys." She put her knuckles to her mouth and sucked on them, wincing.
"What do you have to fight them about?" Sansa fluttered, confused. Arya looked up at her for several moments before answering.
"You wouldn't understand." She paused. "And if you tell mother I will put a snake in your bed this time."
Unfortunately, the ladies of Winterfell hadn't learned the same rules as its people.