Taken straight from the top of Hacker News: Eulerian Video Magnification for Revealing Subtle Changes in the World.

In short, some people have found an algorithm for amplifying periodic changes in a video. I suggest watching the video, the examples are striking.

The primary example they use is that of being able to measure someone's pulse by detecting the subtle variations of color in their face.

The relevance here, of course, is that it's a very concrete illustration of the fact that there's a hell of lot of information out there to be extracted (That Alien Message, etc.) Makes a nice companion example to the AI box experiment -- "Suppose you didn't even know this was possible, because the AI had figured it out first?"