During Dean's first conversation with Michael on Supernatural, one line jumped out at me. Michael claimed that he could use John's body as a vessel because he comes from the same bloodline as Dean, a bloodline going back to Cain and Abel. It's all about the blood. Supernatural fans have been given a clue all along, in the title card for season 5. At the start of every episode, a gush of blood bursts onto the screen over the main title. Blood has always been important on Supernatural, from Azazel dripping it in Sam's mouth as a baby to Sam drinking demon blood to fuel his strength. Now, more than ever, blood is the key. Michael's comment about the bloodline made me ask one important question: if the Winchester family bloodline is the important part, why does it have to be Dean? Sam comes from the same bloodline, so why can't Sam be Michael's vessel? Why can't Dean be Lucifer's vessel? From a bloodline perspective, the Winchester brothers should be interchangeable as meat suits. I haven't quite pieced it together, but I suspect the Winchester bloodline will be the answer to everything in the season finale. The blood in the main title sequence is there for a reason, and while I'm not sure exactly what it is, I have no doubt that there will be blood in the finale. Right now, my best theory is that Dean (or Sa) decides to try something out and says "Yes" to both Michael and Lucifer, creating the ultimate Apocalyptic battle inside of him. I'm probably way off base with that theory, but there has to be something about the blood.