Sometimes Dean forgets how utterly terrifying Cas can be. He's gotten used to him just being Cas. His frumpy, socially awkward, angel friend. If he knows more than the average person, he's not sharing, so it's kinda like he's not all that much smarter. And Dean's convinced that if Cas wasn't always bogarting the fun exorcisms, he could have done it himself (no, really, he'd have figured out something). And maybe everybody has a point that he's taking Cas' excesses of power for granted by using them for trivial things like changing the channel without getting up, and asking exactly how much gross shit is invisibly splattered on the walls of their hotel room, and cheating at "Guess the number of marbles in the jar to win a free soda!" If Cas is more powerful, it's all on different plane of reality that Dean can't possibly understand, and it's all flashes of light and a change in air pressure, so it's kind of like it doesn't exist.

If an angel smites someone in the woods and no one's around to hear it, does that make the dry and ambiguously sarcastic comment about Sam's hair later any less hilarious?

He's Cas, who played I Spy with them all the way from Toledo to Cleavland, and every time it was his turn, the answer was inevitably "Sam's shoestrings." Cas smiled every time one of them guessed correctly, pleased to be included and pleased that his humans were surely the most clever of all monkeys.

He's Cas, who on three separate occasions translated Japanese to English when the anime Dean was watching wasn't dubbed and he was too concussed to read the subtitles. Cas, who once, while Sam was out doing weird Sam things that Dean really should have asked about sooner, took a break from waiting for the Apocalypse and watched an all night marathon of Dr. Sexy with Dean without showing any judgment at all. He listened with infinite patience and actually asked non-irritating questions while Dean explained who everyone was, the level of dickishness each character had shown in the last season, and why dramatic reveals were, in fact, dramatic. They shared a bag of Twizzlers, Dean sprawled across the bed on his stomach, Cas perched next to him on the edge with his feet planted on the floor.

He's Cas, who glared at him in the hotel parking lot and haded over the to-go bag that Dean had left behind at that diner in Scranton.

Cas, who once burned hope through Dean's chest when he leaned into the front seat to demand they repeat a Zeppelin song. Bursting with pride, Dean rewound the cassette, cranked up the volume, and tried not to watch in the rear-view mirror while he waited anxiously for Cas' opinion. (Which never came. The bastard.) Sam, on the other hand, didn't bother keeping his excitement to himself and spent the next hour twisted in his seat, talking about how Robert Plant was a huge nerd (just like Sam!) and trying to convince Cas to join their brotherhood of dorks who were way too into hobbits but managed to still kick some ass on occasion. (Cas didn't give an opinion of Sam's ass kicking skills either. Ha.)

But now, Cas isn't confused. Or contemplative. Or in any way enamored with humanity. He's not Dean's weird best-friend-forever-even-through-rough-patches-which-happen-pretty-frequently.

No.

He is rage.

Rage barely held behind blue eyes and human skin. Rage ready to explode and burn Dean to his component elements of ash and guilt. Rage that lands with the WHOOMP of wings, and pulls the walls in close as Cas strides forward, his form expanding, taking up the whole room until Dean breathes in only wrath. Shadows rise against the far wall, wings black and pissed and utterly terrifying. He is vengeance and flaming, righteous anger and promise of pain, and Dean is so fucking toast.

Shit. Shit shit shit shit.

He trips and stumbles backwards, and before he can right himself, he's thrown against the wall. Pinned in place. Nose to nose with his own furious end.

Doom hits him with the pounding in his skull and the force of Cas' glare, and Dean knows with absolute certainty that there's no coming back from this one. This isn't a hell hound or a shot gun shell or a dumb heart thing. This is Cas, and Cas is going to slam him back into hell so hard he makes a crater from which there's no escape.

Cas shouts, and Dean's not clear what the words mean—the why of Cas' anger—because every statement sounds like torn metal and thunder, and his ears are ringing and bleeding and the pounding of his heart drowns out everything else. The wall quakes, rumbling through Dean's spine, and he expects the room to shatter around him in a cloud of splinters and ripped wallpaper, taking his skin and bones with it.

"Are you listening?"

He struggles to get words past the forearm at his throat. He flounders to get a cohesive thought past the shock that's seized all his muscles and short circuited his brain. He clutches at Cas' wrist and manages to croak an answer. "Sonovabitch."

A split second to understand that answer, and Cas' anger folds over itself, the pressure slamming Dean further against the wall. Cas' face contorts, his eyes burning, boiling the air, his glare stabbing into Dean's mind.

"You'an biteme," he adds.

And Cas snaps. Lashes out. Smacks him in the most expedient, impulsive way possible.

With his face.

The blow lands like a sledgehammer. It sings with a thousand voices, shrill and murderous, visceral and demanding, gravel and fog and heat, heat, heat. Light lunges down Dean's throat, surging, expanding, charging him with blinding, burning power until all he can see is white. It threatens to tear him apart, bursting from every scrape and scratch in his skin. It sears through his veins, pulsing with every wild slam of his heart. It hisses across his skin, his tongue, the stubble on his jaw, like the lightning that seizes his lungs and braces his every muscle for the final blow.

He grasps for something similar, something familiar to ground himself, but everything pales in comparison. The kiss of death in The Godfather. The smug, sealed agreement of a crossroads demon assuring his death with heavy finality. Those are nothing.

Cas pulls back enough for him to feel dizzy, heat still rolling over him in waves, but no longer pressing through him. "You," Cas growls, "make me angry." And that would be an understatement, if not for the fact that it's Cas and therefore deeper than any other sentence ever spoken by anyone ever.

A rustle of wings that booms in his ears, and Cas vanishes, leaving Dean to collapse to his knees and gasp for breath. The air is cold and thin after the force of Cas' rage. The motel room jarringly normal.

He might pass out now. Or maybe just die. Weird that Cas didn't sick around to watch that part.

Dean's still there when Sam shows up, jiggling his key in the lock and stomping into the room. "I've calmed down enough to talk about it, but that doesn't mean I'm not still ticked," Sam says, not looking at him as he drops a plastic bag with a big yellow smiley face onto the table and starts to dig through it. He says something, and again Dean isn't really listening. Then "...Seriously, Dean. I'm traumatized again and—What's wrong?"

Sam pauses to furrow his forehead and realize that his brother is slumped on the floor, marked for death.

"Cas tried to kill me." His voice comes out squeaky, but he's going to blame that on having his throat burned from the inside out.

Sam rolls his eyes and goes back to shuffling through his bag, taking out a plastic wrapped sandwich.

"This is serious."

"Come on, Dean. If he'd really wanted to kill you, you'd be dead."

Dean pushes off the wall enough to lean forward and really get his point across. "No, dude. This was like a warning. Like 'I'll be back in five minutes with my better knife' kinda warning. Or like he was too ticked to even murder me without taking out the whole county, and needs to cool down before he offs me."

Sam unwraps his sandwich, peeling it open enough to make a face at its contents. "Yeah. He'll cool down, then come back and glare at you. And then he'll forgive you like he always does and forget about it." He sounds disapproving of this (entirely hypothetical and unlikely) forgiveness. Like killing his brother is really the best option, but he knows Cas won't go through with it because the angel lives to disappoint.

The whole argument is stupid, because it's not that Cas needs to forgive him. It's that—if he lives long enough—he'll need to forgive Cas.

"He gave me the headbutt of doom."

Sam looks up, mouth full of gross sandwich, eyes lit like he's academically interested in violent death omens and has tons of boring lore to share on the subject. Then his eyes narrow. He steps forward and crouches in front of Dean, finally getting a good look at the damage. "What's wrong with your mouth?"

He reaches up to touch his lips, finding them twinging and bruised. "Fucking Cas."

"He headbutted you in the mouth?"

Finally. Some understanding of how serious and messed up this is. "It's like the dude's jaw is made out of cement."

It must look bad, because Sam looks downright confused. "Wait. He hit you in the mouth...with his mouth?"

"I know! Angels, man!" They can't do anything that's not weird.

Sam stares at him. "That's...either a really bad headbutt or—"

"Seemed pretty effective to me." He prods his fingertips to his jaw, shifting it back and forth to check it's not broken. His face feels sunburned. His lips feel chapped.

Sam gives an exasperated sigh and hoists himself up. "Yeah," he mutters. "Effective. Really got the point across." He crosses the room and slumps down into the chair at the table, planting his elbows to devote his whole attention to his sandwich.

Dean rolls his eyes and forces himself off the floor, swaying a bit on unsteady legs. "Nice to know you care, Sammy." He gives the words an extra snap to cover any residual wooziness.

"It's Cas," Sam says, his eyebrows raised pointedly, like the gesture alone makes it a watertight argument.

Sam would have been a shit lawyer.

At Dean's blank stare he shakes his head. "You're an idiot. I'm back to being mad at you."

Stupid Sam. He's fallen into the trap.

He's forgotten that Cas is utterly terrifying.