Apparently they had found the one thing that left Dean speechless... well, almost speechless, save for the glorious way he was moaning Sam's name. And it really was sexy. Sam would definitely be replaying this scene to himself a lot - most likely while in the shower.
It still wasn't quite enough though. Something was missing. Sam wrapped an arm around Dean and shifted back on his knees, using his height advantage to pull Dean up and onto his lap. Much better.
His lips were instantly on Dean's again, on hand in his hair, the other gripping his hip deathly tight.