“Again when a bird flies in the sky, beasts do not even dream of finding it or following its trace. As they do not know there is such a thing, they cannot even imagine this. However, a bird can see traces of hundreds and thousands of small birds having passed in flocks, or traces of so many lines of large birds having flown south or north. These traces may even be more evident than the carriage tracks left on a road, or the hoof prints of a horse in the grass. In this way, a bird sees birds' traces."