Mysteries of Animal Intelligence

Throughout the ages, animals have played a significant role in human life. But the relationship between animals and humans is often taken for granted. For example, everyone knows that dogs can be trained to sit, stay, and roll over, but could a dog guid a blind man 2,400 miles down the Appalachian Trail -- a difficult feat for a sighted person? Could a cat actually defend a sleeping infant from a deadly rattlesnake that is prepared to strike? Could a dolphin really save a person who is drowning at sea? Could a monkey communicate using English?