A fox was walking along a hill one day when he happened to glance up and he saw a cloud scudding past.  Thinking the cloud was something to eat, he began to implore it to come down in the usual way he used with birds and other such animals.  "Why don't you descend and walk with me in this pleasant meadow?" he said to the cloud.  "We can laugh and play all afternoon, and in the evening you can come back to my warm den with me."  And he continued in this vein, following the cloud as it sailed through the sky.  He walked all day, pleading and wheedling, but he never got any closer to his prey and at sunset he found that he was lost and just as hungry as he had been when starting out.

All predators eventually meet prey that they cannot catch or fool, no matter how hard they try.