Before Aang, that response might have annoyed him, but now it makes him nod. Good attitude. Practical, survivalist, willing to kill if she needs to, if she has to skills to back it up - or is willing to learn what she can in a week - she might be a contender.

He gives a one shouldered shrug at her comment. "Used to be. Different now."

If he realizes that she's angling for an explanation, he doesn't give any indication of it, but it's fairly obvious he's not a big talker.

"Gonna need to. Know how?"

Maybe that should have been his first question, but as far as Derek's concerned, being willing to kill is more important than knowing how.