Human beings are simply not equipped to pick up any of the stimuli that provoked these responses. Many insects, for example, can see ultraviolet light. The runaways followed by bees as they land on flowers are ultraviolet patterns that lead them to nectar. Pit vipers, on the other hand, can sense infrared radiation or warmth with the help of their additional `pits' situated between the eyes and the nostrils. The pits enable them to locate prey by the warmth radiated from them. Goldfish, like many freshwater fish, can see light far into the red end of the spectrum. This is because they live in rivers and streams that turn a rusty red in the presence of fallen leaves. They cannot, however, detect the infrared radiation `seen' by pit vipers.

The mouse can detect the ultrasonic squeaks of her babies which are inaudible to the human ear. The moth takes evasive action after detecting the bat's presence from the echolocating ultrasonic squeaks of the bat, just as dogs respond to dog whistles. At the other end of the sound spectrum, below the range of human hearing, elephants hear and communicate with very low frequency sound-infrasound. The superior sensory abilities of all these animals reveal to them aspects of which man is completely unaware of.

[II] The eyes of some animals are made of structures with thousands of lenses. A jumping spider pounces nimbly on an insect. A dragonfly twists in the air to take a tiny fly. A flying eagle searches for its prey from a great height. For all these animals, keen vision is absolutely essential to sustain their ways of life and are therefore endowed with superior vision. Their eyes are of different designs and abilities, which help them cope with problems such as navigation, recognising objects and finding food.

The most primitive form of `eye' in the animal kingdom is found in some unicellular animals. Their minute light sensitive eye spots can only tell them the direction from which light is coming. The simplest `true eyes' that is, eyes that form images are found in various kinds of worms. These eyes are just pits, without lenses, but lines with light-sensitive pigment, giving a crude picture of the world, sufficient to detect the approach of a predator, and little more.

Insects have compound eyes, which consists of a large number of tiny hexagonal units. Each unit has a lens that focuses light on light-sensitive cells behind it. This provides a much more sophisticated view of the world than what the worm sees. Dragonflies, for example, have a single lens for each eye, which means that they see the world just as we do. Even so, the larger size of our eyes makes our vision six times clearer than theirs.

Many birds, however, have sharper eyes than human eyes. Eagles and other birds of prey depend on their eyes, which magnify their view to spot objects from far. Their ability to distinguish objects from a distance is believed to be two to three times as good as ours.