The word kangaroo comes from the language of the Aborigines, Australias indigenous people. It basically means I dont 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.