WARNING: SPOILERS for the most recent SPN episode (episode 17)

A/N: This is a tag to s13e17, at the beginning of the episode where Dean puts the post-it notes on Sam's back. I was honestly waiting for Cas to turn up and wonder what the hell was going on, but he didn't, so I wrote this!

#2 - Post-it Notes

If there was one thing Castiel didn't understand about the humans, it was the incessant jokes that they - namely Sam and Dean - played on each other.

To say he'd been confused when he'd teleported to the bunker directly behind Sam and seen the post-its stuck on his back would be an understatement. He frowned.

"Hey, bud," Dean said from across the room, sipping on his coffee.

"Hello, Dean," the angel replied. "I, uh-"

The elder Winchester looked confused for a moment as he watched his best friend tilt his head to the side and continue to stare, completely perplexed, at his brother's back, until realization hit him in the face. He made the mistake of snorting into his cup, coffee immediately splashing out and onto the table.

Both Cas and Sam looked at him. "What is it?" the hunter asked, and Dean shook his head, trying - and failing - to cover up his grin as he cleaned up the spill.

"Nothing, nothing," he assured his brother, turning in his seat to look up at the angel. "You alright, Cas?" he asked as a way to steer the three of them off the topic.

"I am fine." He was still staring, and Dean was starting to wonder if Sam would ever-

"Cas, what the hell are you doing?"

-notice.

Cas looked at Sam. The man had turned a bit in his chair, and had seemingly realized that the angel had been there the whole time, apparently... staring at his back?

"I am confused."

"Why're you confused?"

Cas's frown deepened and he lifted his head to look at Dean, who made some weird hand gestures and then returned to drinking his coffee when his brother spun around to look at him. He glanced back at the post-its before stepping forward and hesitantly kicking Sam under the table.

Sam yelped and turned to glare at the angel. "Cas! What the hell, dude? That hurt!"

"I'm... sorry. I thought-"

The younger Winchester was looking pointedly at Cas, ignoring Dean's unrestrained laughter and failed attempts at trying to cover it up. "You thought...?" he prompted.

The angel shook his head as if trying to remove the thoughts that were currently racing through his mind and took a deep breath. "I'm sorry, Sam. Forgive me."

Sam frowned. "Yeah, okay..."

Cas smiled grimly before turning to walk towards a chair at the table. He sat down and looked at the brothers. "Have you found anything on the Seal?" he asked, and Sam shook his head, still looking concernedly at the angel.

"Uh- not yet, no. I've been looking through books, countless websites on my laptop... I mean, we could all try looking through the archives but I doubt there'll be anything there. This whole Seal of Solomon thing seems to be very secretive, and I don't-"

"No, I'm sorry," the angel interrupted him, moving restlessly in his seat, "I need to know why you'd say that about yourself, Sam."

"Say- say what? Cas, what are you talking about?" Okay, he was starting to get worried now. That angel had been acting strange since he teleported his feathery ass into the bunker! What was wrong with him?

Cas looked positively distressed, staring at Sam with such confusion in his eyes that made him raise an eyebrow and scoot his chair closer to him. "What is it?" he asked, looking questioningly over at Dean, who shrugged and started laughing into his coffee. What was so funny?

"You are not stupid," the angel said, grabbing hold of the younger Winchester's hand and enclosing it in his. "You are Dean are the smartest people I know. We will find the Seal, we will rescue Mary, and we will find Jack. Together. Don't doubt yourself, Sam. And, what's more, don't write it down and stick it to your back! That's really going a little too far-"

"Stick it to my- Cas? What the hell?" Sam said. He frowned and yanked his hand out of the angel's grasp, grabbing the back of his shirt and immediately growling once his fingers made contact with a post-it note. He pulled it off and stared at it. ASS FACE.

"Dean!" he said exasperatedly, trying to twist his shirt around in vain to see if there were anymore there.

Dean was in stitches, bent over the table and laughing hysterically. Cas couldn't remember a time he'd been so happy. He glanced confusedly over at Sam and took the post-it from his hands, looking at it and tilting his head slightly to the side. "You wrote these notes and stuck them to Sam's back?" he asked, twisting his head to look back at Dean.

"Yehes I dihid!" the hunter replied, face a bright shade of red as he attempted to compose himself. "Ahand you made it tehen times behetter, mahan!"

"Cas, how many more are there?" Sam asked, lifting his legs and turning in his seat. The angel rolled his eyes at the joke his mind had finally caught up with and reached out, pulling off the three remaining post-it notes from the man's back.

He handed them to Sam and watched with wide eyes as the hunter grew increasingly furious. His eyes scanned the words. I'M STUPID. ASK ME, KICK ME, and DUM DUM.

"Wow, Dean," he said, glaring at his hysterical brother, "real mature."

"Oh, shut your mouth, ass face," the older hunter said with a wink, and Sam was up and out of that chair in a matter of seconds, chasing after Dean.

Cas stayed still for a moment, trying to figure out what had just happened. After a few seconds, he gave up, grabbed Sam's laptop and shook his fondly at the happy shouts that were echoing around the bunker.

Humans, he thought to himself with a chuckle. My humans.