Sirius catches the look and it makes him curious. He figures the guy is human, and can't really smell anything to the contrary. If he were smarter, and listened to the reasonable voices in the back of his head, he would figure that now would be a good time to break off the conversation, bid him farewell and disappear to (hopefully) not be seen again. Or for a while at least.

But leaving well enough alone was not something he'd ever been good at.

"Seen some things?"