And yet the eagle will sit for hours on the crag and survey the kingdoms of the world until it spots a distant movement and then it will focus, focus, focus on the small shell wobbling among the bushes down there on the desert. And a minute later the tortise find the world dropping away from it. And then the eagle lets go. And almost always the tortise plunges to its death. Everyone knows why the tortise does this.
Gravity is a habit that is hard to shake off.
No one knows why the eagle does this. There's good eating on a tortise but, considering the effort involved, there's much better eating on practically anything else. It's simply the delight of eagles to torment tortises. But of course, what the eagle does not realize is that it is participating in a very crude form of natural selection. One day a tortise will learn how to fly.