Every animal, in order to survive, has to solve a conundrum: how to eat without being eaten. It has to pay precisely focussed, narrow-beam attention that is already committed to whatever is of interest to it, so as to exploit the world for food and shelter. Put at its simplest, a bird must be able to distinguish a seed from the background of gravel on which it lies, and pick it up swiftly and accurately; similarly, with a twig to build a nest.
