Dean's learned that Castiel's noises never have a single meaning. They're more complex than any human word is capable of being. He's also learned that, though he's getting an idea of a good number of the noises, they can change their meaning slightly when they're used with other noises or in a string of noises.
Which is why Dean's having a hard time not laughing hysterically in a library. Cas is going to get them all kicked out. Well, he's going to get Dean kicked out. Sam can't hear anything from Cas, has no clue what's going on, and Cas could put Clint Eastwood to shame with his poker face.
*Huff, trill, huff, huff*
Dean covers his mouth with his hand as he continues pretending he's reading some kind of book that Sam set in front of him and told him to skim. Dean doesn't even know what the book is about. And he doesn't care at the moment.
While the trilling noise is normally a call out to someone, followed by the noise specifying who Cas is calling out to, using the trilling noise in conjunction with the huff they carry the meaning of Cas calling out to anyone who will listen that he's very bored.
*Trill, huff, huff*
Dean glances over at Cas, but Cas is stoic, looking at the book in front of him. Dean doesn't know if Cas is reading it or just pretending because Cas is just that good.
*Huff, chi, huff*
Dean can't help it. A noise one might expect to hear coming from a wounded buffalo breaks free from him. Sam's head snaps up, a scowl on his face, and Dean flaps his hand in Sam's direction.
“Sorry,” Dean whispers, then goes back to pretending he's reading something very interesting, which is very hard considering the book wouldn't even be interesting if he was actually reading it.
*Chi* refers to death and/or dying. The subtle inflection in *chi* lets Dean know that Cas is joking. Which is something else that's new to Dean as of late. Dean has discovered that Cas is damn funny.
He's learned that angels aren't humorless dickbags. For the most part. It's just that they're more subtle about their humor. And sometimes very sarcastic.
Like right now. Cas is calling out to anyone that'll listen, complaining about how he's so fucking bored he's going to die of said boredom. Dean knows the feeling, but the fact that it's coming from Cas and that Sam has no clue what's going on is tickling Dean's funny bone.
Dean lets out a bark of laughter, and this time there are several people around them who shush him. He manages to cover his mouth, but his shoulders are shaking and he's trying to think of something really un-funny to stop the laughter. It's not working.
Not only is Cas cracking him up, but he's in a library, and knowing he's not supposed to be making noise always makes it harder to keep from laughing like an idiot over even mildly funny things.
“Dude, what is so funny?” Sam hisses at him.
Dean shakes his head no, his eyes still on his book. If he looks at Cas now, he'll laugh again, most likely even louder than before. He knows Cas would look at him like he's completely surprised Dean is acting like such a child in the library.
Sam rolls his eyes, huffs, and goes back to reading his own book. Dean nearly giggles at Sam's huff. If Sam only knew what his huffs mean in the language of angels, he'd pull an epic bitchface.
Dean buries his face in his hands, snorting and shaking with laughter, his stomach, chest, and throat burning with the effort to keep quiet.
“Either knock it off or leave, jerk,” Sam hisses, his eyes wide.
*Huff, eh, chi*
There are tears leaking from Dean's eyes. He's making a wheezing and whining noise, still trying not to laugh, but failing miserably at even keeping remotely quiet.
Dean loves that Cas is this comfortable with him. Telling Dean that his brother is so fucking boring that they should kill him is such a refreshingly fun thing to do, and Dean almost wishes other people knew this side of Cas.
“Dude!” Sam hisses even louder.
“Come with me, Dean,” Cas says, and Dean would jump in surprise at how suddenly close Cas is to him, but he's too busy laughing.
Dean feels a hand on his right upper arm, and he stands up, letting Cas lead him out of the library, people giving him dirty looks as he stumbles along. Dean lets out some pent-up laughter once they get outside.
“You got me in trouble on purpose,” Dean accuses through heaving laughter and giggles.
“Did what?” Cas asks, all wide-eyed and innocent.
“Earned us a few hours of alone time while Sam slaves over a hot stack of books,” Dean says, grinning and wrapping his arms around Cas.
Cas blinks at him. “I don't see why you're accusing me of purposely getting you in trouble when you've gotten what you wanted in the first place, and now I get to take you back to the motel room and do very fun things with you.”
Dean's eyes widen and his dick twitches. “Fuck, yeah, let's do that!” he blurts, pulling out of the hug and grabbing Cas by the arm, dragging him toward the car as Cas just grins.