It was a trap. One which could have been fatal, if their reflexes weren't as good as they were.
The witch they were hunting had set up a triggered trap, just before she had fled.
As they opened the door to her apartment, it prompted an explosion. Not too big - it didn't cause any damage to the structure of the whole building - but it was large enough to smash the door into pieces, the debris catching the three men.
With lightening-quick reflexes, the Winchesters and Castiel threw themselves out of the way of the major line of fire - the large splinters of wood behaving like bullets.
Luckily, the only damage to the men were a few cuts.
At least, that's what they believed.
—
After looking around for any clues as to where the witch may have disappeared to, with no results, the trio made their way to the diner nearby to the motel they were staying in.
They sat around the table, with Dean eating a massive bacon cheeseburger, Sam a salad, and Castiel a small plate of fries.
The fallen angel barely spoke, picking at his food, not paying much attention to the brothers.
No one said anything, but the Winchesters were worried.
—
Turns out their worry had been for a good reason. Though no one had worked it out until they got back to the motel later in the evening, blue-eyed man in tow.
When Cas took off his trench coat, he revealed the line of blood along his side.
They checked, hoping that there was very little damage, but unfortunately it was bad.
Cas's side was torn apart, by one particularly nasty wood chip.
"Cas, man, if you're hurting, you gotta tell someone!" Dean explained, trying to talk to keep himself calm, but he couldn't reduce the damage already done.
—
Cas gets stitched up by Sam, while the blond paces impatiently beside him.
Instead, the blue-eyed man waited patiently, ignoring the pain resounding from the wound.
His eyes water slightly, as the pain toes the line of unbearable, but he doesn't make a sound.
"It's okay if it hurts, Cas."
"I'm fine."
The blond heaves a sigh, and goes back to pacing.
—
The angel ends up dressing in a t-shirt and pair of jeans of Dean's. The t-shirt is slightly too big, and hangs loose on his shoulders, but with his perpetual bed-head, he looked cute.
Dean almost shoots himself for thinking that.
—
When the wound fully heals, Cas is left with a scar, and a few week's worth of Dean running after him, caring for him.
It was even better than being in heaven.
So, to say thank you, Cas gives the blond a kiss. Which Dean immediately deepens.
'I stand corrected,' the fallen angel thinks, 'this is better than being in heaven.'