Sam reads over the words a few times before heading off to drop the book in front of Dean. "Looks like I found it," he says grimly. "Not that it makes a lot of sense. I mean...if anybody was going to get hit with this, you make a lot more sense."

Because Sam doesn't think for one moment that Castiel wouldn't do that to protect Dean. And the one being who MIGHT have done it for Sam? Well, he's been dead a long time.