The twinge in his back means that Sam does. That he absolutely understands why he won't talk about it.

"I mean. Kinda shitty that she didn't tell them the price. At least demons tell you that much." He reaches back, rubbing at his lower back for a moment before he lets out a breath. "They didn't pay it, though, did they? They probably would have been fine had it been one of their lives that the woman wanted as payment, but not one of their kids."

Because that's how it works. Sacrificing yourself is one thing. Sacrificing somebody else? Well, most people wouldn't do that.

Most. Some people are all too willing to do that.