Cas may not be the most tactful guy in the world (can we say vast, vast understatement?), but even he can tell that conversational gambit fell more than a little flat.

Feeling somewhat sheepish even if he doesn't look it, he offers a lame and somewhat stiff half-wave to Philip, and follows Dean. Dean doesn't look like he's feeling well. And Cas suspects they need to talk, if he read Dean's look correctly. Perhaps Dean disagrees with his Nephilim lore?