Elephants are the world's largest land animals, with African Savanna elephants standing up to 3m high and weighing up to 6,000kg on average. Their trunk has around 150,000 muscle units, making it the most sensitive organ in any mammal. Elephants' tusks are actually enlarged incisor teeth that first appear when elephants are around two years old and continue growing throughout their lives. An elephant's skin is 2.5cm thick in most places, and the folds and wrinkles in their elephant skin can retain up to 10 times more water than flat skin. Lastly, elephants constantly eat, consuming up to 150kg of food daily, amounting to three-quarters of their day.