[ Well, Sam is about to find out what it has to do with, because Castiel immediately steps forward and grabs him by the throat, not hard enough to actually choke him, but with a grip that's unbreakably strong, by human standards. ]

Listen very carefully, Sam. If anything happens to Dean— if he's killed by anyone or any thing in this universe, I don't care who it was, or how it happened: I will take it out on your ass.