He can't help but bristle a little at being touched without much warning; it's not that he doesn't like it, but it always sets him on edge when someone who doesn't know about the other guy starts poking around in his space, at least until he gets a chance to adjust to the idea.

Once Mina puts his hand against her "pulse point", the contact isn't the only surprise he has to deal with. His expression evens out from one of mild discomfort to curiosity, and then concentration as his gaze slips away from his hand and he palpates, looking for the pulse he knows isn't there.

"So what does this mean?" he murmurs finally, taking his hand away. He glances back at Castiel briefly, in case he's in on this too, before he turns back to Mina. "Other than that you should be dead."