We've all played the "Wait, who is that guy again?" or "What song is that?" while watching a movie. Now, with the latest update to the Play Movies app, if you want to get the answer to that question, all you have to do is press pause. Info cards will then pop up with face recognition of actors on screen, what other movies they're in, and what music you're hearing.
The feature only works on "supported movies" and it's a little unclear which ones those are (there doesn't seem to be any icon or indicator that shows whether any given movie in your library can show cards).