Castiel has never locked a door.

In fact, he has never felt the necessity to- even to take care of is new infuriating human needs that make him extremely embarrassed (Dean is just the opposite, standing up from his chair, putting his beer down, and proclaiming, "I'm going to go take a piss." Sam finds this incessantly annoying.). The Winchesters have an if-the-door-is-closed-knock rule, which is followed with religious-like tendencies, because, according to Sam, no one wants to walk in on Dean shitting.

But today Cas locks the bathroom door anyway, because today he has a need.

He has learnt, in his three short months as a human being, that aforementioned species can get hurt by anything. Opening the front door, reading the newspaper, cooking a meal- anything and everything has the possibility of an injury hidden beneath it.

Cas has also discovered- to Dean's mirth and his dismay- that he is quite the clumsy human, and manages to exhume every bruise and scratch possible from human activity.

The former angel braces himself against the sink with one hand and runs the other over his face, feeling the sandpaper of the stubble on his jaw with his palm. He brings that hand down to his neck and snakes off his tie. His trench coat falls to the floor- fwump- and his shirt joins it with a hiss as it falls from his shoulders.

Castiel's entire torso is dotted with scars (which he finds irritating considering the absolutely domestic life he is living). Most of them are petty- puckered skin along his hip from when he had leant back against the hot stove) "Not a smart move, Cas," Sam had exclaimed); a faint white line on his wrist that he had gotten as punishment for opening a switchblade in the wrong direction; four parallel red lines from slipping in the not-generous shower and finding Dean's razor under his palm. The latter of these would probably disappear in a week- "Only," Sam had said, as if talking to a child, "If you stop picking at your scab!"

Scab- what an ugly word, and terrifyingly mundane. Cas is used to his wounds closing up before his eyes. Of course he has had worse than this tiny cut, but never has he had to deal with something as human as a scab.

Other scars had been intentional- like the first and only time Sam and Dean had taken him to a bar as a human, and dragged him back out to the Impala an hour later because of course he was a lightweight and of course there had to be a thug with a hunting knife in his belt; or the time he had gotten a bit too snappy with Dean about a week ago. Those bruises are just starting to yellow.

And then there are the scars he doesn't want to look at; the two that will never fade; the scar tissue he will always feel when he flexes his shoulders-

No.

Castiel has never been vain. It is not in an angel's nature to be so, but after all, he isn't an angel anymore, and he could stand in front of this mirror all day and find more things to hate about himself.

How very like a human.

His heart leaps into his throat when someone raps on the door, curling his arms around his torso. Dean's baritone drifts through the wood. "Sam, you've been in there for twenty minutes and I know you're doing something unnatural to your hair-"

Cas clears his throat- another thing he hadn't needed to do before. "No. It's me."

There is a silence and Dean speaks. "You didn't fall in, did you?" he asks jokingly.

Cas glances at the toilet, confused. "How could I-"

"Nevermind," Dean interrupts. Cas can almost see him testing the door knob with his fingers. "Are you…okay?" He hesitates before the last word, and Cas knows it's because "okay" is rarely an adjective used for anyone under a Winchester roof.

Cas sighs. "…No."

Dean hesitates for so long Cas thinks he may have left. "Can I come in?" the hunter asks finally.

Cas doesn't reply, just twists the lock and tries not to wince as Dean crowds into the small bathroom. For a moment their eyes meet in the mirror- one pair of deep blue, one of bottle green.

Then Dean does what Cas has been hoping he wouldn't, and looks at his back.

"Damn," he mutters under his breath. "Are those what I think they are?"

Cas mimicks Dean and shrugs. After a moment of silence he speaks. "They're awful, aren't they?"

Dean points at his back. "These?"

"All of them," Cas says.

"I don't know," Dean replies, tilting his head in such a way that he looks remarkably like a puppy. "I think they make you look human."

Cas blinks- Dean says the word almost in reverence. "Is that a good thing?"

Dean squints, as if trying to decide how to respond. He opens his mouth, closes it again. "Yes," he says finally. "Right now, yes." Suddenly he lifts a booted foot to Cas' hip and shoves him into the hallway. "Now get out and stop pouting. I have to piss."

Sam emerges from his room just as the bathroom door slams shut. He takes in Cas' dazed look and half-naked state before his eyes are forced shut by a jaw-breaking yawn. He waves a hand at Cas and begins down the corridor to the main room. "I don't even want to know."

Cas realizes no one knows how human he really feels except Dean.

And strangely, he doesn't mind.