Dean gives Sam something he's made. Sam gives Dean something he's kept for a long time.

Dean settles down, Sam finds him, they settle some things.

Sam loses Dean; Sam never loses Dean. Sam lets go; Sam hangs on.

Dean tries to fix Sam. Talks ensue.

It’s not like Dean never noticed Sam’s hands before. He’d taught Sam to pull a bowstring and a trigger and tighten a lug nut. He’d watched him obsess over his homework night after night, always holding the ballpoint a bit too tight, flesh whitening over his knuckles, as though someone was going to take the pen away. 

Dean didn't even realize he was doing it. Really. The whole heart thing was totally not a thing.

In hindsight, getting his hallucination-prone, caged-for-nearly-two-centuries brother trapped underground with things he can’t see may not have been Dean’s best move.

Dean knows too much about koalas and tops the hell out of Sam. It ends well.