The African impala is a deerlike creature that can jump to a height of 3 meters (nearly 10 feet) and cover a distance greater than 11 meters (36 feet) in one bound. Yet the impala can be kept in a zoo enclosure with just a 1-meter-high wall. Why? Because it isn’t tall enough to peer over the barrier, and it won’t jump if it can’t see where its feet will land.