Castiel smiled faintly at Meg's insistence that Casablanca was one of the greatest films ever made. He could see her face, her true face and he still found her beautiful, but it was learning things of that nature about her that helped that grow deeper. That thorny pain he talked about, that was something she never showed others and instead let be known when she was around him, albeit briefly. And while he didn't know much about popular culture, not much outside of what he'd learned from the Winchester (and even then he was still lost, more often than not) this was something different.
The film had his rapt attention, something that never wavered as it was on, although he began to close that gap between them. Not completely, just subtly, as he drew in closer to her. They weren't nearly as close and intimate as they'd been when they watched television together just nights prior, but that didn't draw away from the fact he kept getting closer to her, making that chasm between them just that bit smaller and smaller as the movie continued on.
"But..." he began, when the film was over, thanks to the ending, when Rick forced Ilsa onto the plane. He'd given up things before, like rebelling against his orders, his family, to serve the cause that the Winchesters opened up to him and while he didn't completely understand how human emotions worked, it was still something that upon his features was proof he didn't like how the film ended. He did however, seem to enjoy the older film, as opposed to how he would have reacted to the newer, flashier movies that he likely would have been exposed to by the Winchesters.