It was becoming more and more obvious that Kate didn't want to explain herself to him. He could understand that, as curious as he was about the matter. After all, Sam was the one who had been hiding the truth about himself from everyone else for such a long time. Even now, he was still very wary of people discovering the truth about what he was capable of and what exactly was inside of him to boot. So even though a large part of him was sorely tempted to keep pressing the issue, Sam decided to let it go for now. It wasn't all that important, was it? She wasn't a threat - even though his instincts argued otherwise because of her face - and she wasn't getting on his case about his abilities (not that Sam was sure she even knew about them) so all was fair. He'd let it go for now.
"If they have some of their fathers in them, there's probably a need for chaos somewhere too." Sam was only saying that because he wasn't stupid. He had demon blood in him and sometimes, with the way that he thought about things, he wondered if he got more than just the powers when Azazel came to him in that nursery. Was there something else he was missing? Ruby didn't seem to think so, but one could never tell with her anymore anyway. "No demon in you," Sam repeated, looking somewhat curious, "all right then." Then what was? She clearly had something going on with her. He had promised himself that he wasn't going to keep questioning her on the matter, so Sam zipped his mouth shut and turned to look at the building once more.
"You think you can handle demons?" Sam reached into his jacket, pulling out his fake FBI badge. "If so, I don't mind you coming along. Dean and I agreed a while ago that we would bring those who wanted to join hunting with us if they wanted. Good way to teach you all for the stuff that you'll probably end up facing with or without us in the future." Sam glanced back to her, snapping his badge shut once he was sure he had the right one. "It's up to you."