Random thought about the end of 4.10 that everyone else has probably already discussed.
It occurred to me, during the end scene of 4.10, Dean kept calling Sam Sammy. Now, that stood out for me as a bit awkward, and a bit... hm. Something not settling right about it. So, here's my scrambled thoughts on it.
Dean's obviously distraught. Like hugely. He's calling Sam 'Sammy' and deliberately not looking at him. The only way he can let this out is not looking at Sam. Sammy is an endearment, a family callback to their younger days, Sammy is the innocent Sam. Not the Sam who wants Lilith's head on a plate, not the Sam who tries to access powers given to him by the demon who killed their mother, not the Sam who has a demon as a mentor. He's talking to innocent, twelve year old Sam who is still inside, who Dean has to believe is still inside his brother. The one that needs him and the one who needs his protection and care.
Thing is, what he's saying at the end of 4.10 is the very last thing he'd want to burden his brother with, and the last thing he'd want to admit, and stain what's left of the innocent Sam. But in a way, not conciously, but in a way... I think he's calling Sam 'Sammy' to get him to realize Sam is still in some part the bratty little brother Dean gave the last of the Lucky Charms to, to ground him. Or something. I don't know.
I think it's also because, well, Sam is what breaks Dean. He'd made the Deal for him, he probably broke in Hell to protect his brother. Dean's worked his whole life on keeping Sam safe and as much as possible, to keep him innocent. He needed Sam to still be that pudgy 12-year-old. Not this psychic-powered dangerous person, affiliating himself with demons. Dean's not speaking to the adult Sam there, he's speaking to his little brother, one who maybe in Dean's mind can still be kept innocent if Dean tries hard enough.
Gah. Does that make any sense?