Sammy's growing.
Dean can see it- watches Sam's bones stretch and the muscle pile on. He's all gangly, too-long limbs and awkward shifting. Dean can remember going through it himself, as he watches Sam grimace at the twinges and aches. Though he remembers a less painful and more gradual process.
Sammy's growing up.
He knows it, hell, even Dad knows it. He watched his father's eyebrows shoot up as Sam climbed out of the Impala during a rare pit-stop. Watched his eyes rake up the long lines of Sam's spine and the awkward splay of his limbs, sees the realisation hit in the moment Dad notices that he has barely an inch on Sam, now.
Sammy's growing up fast.
One time Sam misses a week of school in the little town they're staying in, due to a Black Dog bite that tears his hip up. He has to rest on his side the entire week, and when he finally unfolds himself and stands up, Dean thinks Woah. Sammy just smiles through his curtain of floppy, too-long hair that is growing only slightly faster than his height.
His first day back at school and the teachers do a double-take, look on with wide eyes as he trudges in. Dean watches from his position leaning against the car, feels something heavy settle in the pit of his stomach as he notices that Sam's head clears the rest of his classmates', that Dean can watch him through the crowd of crammed-in students right up until the point where he turns back for just a second, with a small little smile that doesn't quite sit right on his face. He doesn't fit here.
Dean's known it for a while, felt the same kind of alien detachment when he watched his normal classmates go about their normal lives. Somehow, it feels wrong for Sammy to know the feeling.
Sammy's growing up too fast.
Normal kids don't know how loud a gunshot really is, the way it rings in your ears and rattles around in your head ages after the initial blast. Normal kids don't know how to patch a bullet wound or stitch an arm back on. Normal kids know that salt is for their mother's undercooked chicken, they've never had to draw a line of it on the ground or load it into a shotgun to save themselves from a vengeful spirit.
Dean knows this, grew up with this. It's a fact, in there with spiders not being actual insects and tomatoes being fruit.
It isn't until he listens in on Sam on the phone one day, stringing together an elaborate tale -involving clumsy footing and stepladders- to explain his dad's absence from the parent-teacher interviews, that it really hits home. Sammy knows all this too. Knows it as sure as the sky is blue and the moon's not made of cheese.
Sammy's growing up too fast [for Dean].
It takes another year and another brush with death in which Sam is strong enough to fling off the creature they're hunting and Dean's not, for it to really sink in. Sam slings Dean's limp body over his shoulder and sprints out of the clearing like he's carrying a bleeding potato sack and not his cut-up brother. Dean looks dazedly at where Sammy's palm is resting warm and huge on his back to keep him in place.
Maybe it's time he accepts that he's not really Sammy's big brother anymore.
