Antelopes communicate through various noises and their horns can grow up to 5 feet long. Llamas are intelligent and can be trained, and are known to spit when threatened. Hippopotamuses are more closely related to whales and dolphins than other land mammals, can bite boats in half, use their yawn to threaten, and have killed more people in Africa than any other wild animal. Cheetahs were hunted by humans as early as 3000 BC and can reach speeds over 60 mph. Camels store fat in their hump, have teeth adapted for dry climates, and can survive for days without food or water.