What if you could just look at someone's face and tell how fast his or her heart is beating?

The question isn't as far-fetched as you might think. The movement of our beating heart inside our chest can in fact reveal itself on the surface of the skin, albeit too faintly for our eyes to see. But as you can see in this video, it's not too faint for a computer (fast forward to 1:25 and 3:18):