The five senses which are our window on the world, which give us all of our sensory experiences, depend on just four types of detector cells—sensitive to chemical substances, to light, to temperature change, and to mechanical distortion. However, the human sensory system provides information about only a small fraction of the forms of energy and chemical events around us. This program looks at some of the sensory experiences of animals that humans can glimpse only through physical instruments of detection and measurement: rattlesnakes use infrared detector organs to sense the position of their warm prey; many insects can sense the plane of polarization of light; bats use ultrasound echo-location to guide their flight; many fishes have electric field organs; and bacteria and birds have magnetic sense. Animals appear to have the senses they need in order to survive. (60 minutes)