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 tortoise finds the world dropping away from it. And then the eagle lets go. And almost always the tortoise plunges to its death. Everyone knows why the tortoise 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 tortoise but, considering the effort involved, there's much better eating on practically anything else. It's simply the delight of eagles to torment tortoises. 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 tortoise will learn how to fly.