Let us start with a series of diagrams showing a predator chasing prey. We
have drawn the diagrams as snapshots in successive moments of time, showing
the positions and movements of the predator and the prey. The arrows show
the directions in which they are running. We assume that the predator is
guided by his perception, i.e. he runs directly toward the prey. To simplify matters,
we assume that the prey continues running in a straight line. We also
assume that the predator runs approximately twice as fast.
Successive sightings of the prey leads the predator in a curved line. The
predator must follow such a curve if only perception is used as directional guide.