blacklid and tahirire have been doing screencap recaps for the past season or so, and blacklid just finished her take on 5.16.
What I want you to take note of (though the entire recap is very good and very thinky--plus squee) is a theory she has in the second part of her recap.
Because if she is right? We know what Dean's "Bloody Mary" secret might be. And this makes so much more sense of out of one particular scene. And some of Dean's issues in general. (Also read the comments on the post, for more theorizing, both cracky and not so much.)
(I know Show sometimes does things that would be cool without realizing it and not on purpose. This is still interesting...enough so that I hope it was on purpose.)