Dean never liked birds. He never could quite understand what people found cute about them. To him, they seemed weird - cold little creatures with these creepy twinkling tiny eyes. Not to mention the hollow bones.
He remembers feeling the same way about angels the first time he encountered them. Apart from the fact that they were real dicks most of the time, there was also this... this thing, some called it the Grace, he thought - something that made them sort of... aloof. He hated the way they just observed him and Sammy and then made decisions and fucking assumptions without ever second-guessing anything.
Then he saw them doubt. Well, he saw Castiel doubt. All of a sudden, an angel - a being he had until then considered... fucking scary, to be completely honest - showed a human side. So Dean encouraged it, by God, did he encourage it, and he watched Cas become first a doubter, than a rebel - and, somewhere along the way, his friend.
Watching birds fly always made him sick. He hated flying, and those little buggers just... fluttered their wings and they were off. He spent some time just trying to imagine what it would look like, an angel flying. He supposed they sort of flew when they made their quick exits and entrées, but he never found that particularly convincing. But then again, Cas pointing a fist towards the sky and taking off like Superman would probably hurt his eyes more...
Because that's it - these days every time Dean thinks of Cas, he doesn't think of Purgatory. He doesn't think of his betrayal, or his bloodied face when he finally came to ask for help; or his suddenly very frail frame when he walked into that lake. Dean forgets his own guilt and thinks of flying. He dreams of flying. He dreams of large white feathers and wind in his face and the ground far, far below him. Strangely enough, it doesn't scare him. Strangely enough, he knows that the eyes watching the teeny tiny houses and fields and thin blue ribbons of rivers hundreds of feet below, are not his eyes. They are Castiel's.
And then Dean remembers all the times Castiel would enter his dreams and he wonders if, maybe, the dreams he is having are not his own. Maybe he's just eavesdropping. Maybe, just maybe, wherever he is, Cas is flying.