After Sam gets his soul back, Dean's become even more mother hen than usual (always watching Sam, asking if he's okay, even the occasional "non-chick flick" hug or pat on the back). Sam, still in his 5x18-5x22 mindset because of the wall blocking his memories, is extremely confused. He can't understand why Dean's so, well ... brotherly, after their downhill relationship the last couple of years, but he can't bring it up in case it makes Dean's behaviour stop. Bonus for Dean figuring this out without Sam telling him and assuaging his fears.