The word "kangaroo" comes from the language of the Aborigines, Australia's indigenous people. It basically means "I don't understand", which was the answer given to British navigator James Cook when he asked what the animal was. What a misunderstanding! These marsupials have a kind of rubber band in their hind legs. It propels them upwards with each jump. The faster a kangaroo bounces, the farther the animal is "catapulted" forwards, and the less energy it consumes. Even though it can achieve a breathtaking speed of 64 km/h, there is one thing it cannot do: walk backwards.