Adult hippos can sleep underwater, and their breathing instinct makes them show their noses from time to time, but in the process, they will not wake up. Although hippos live in water from birth, they can't swim. They only walk underwater, and they are very fast. They can walk about eight kilometers per hour and breathe every five minutes. Hippos' inability to swim has a lot to do with their bone density and weight, but their streamlined bodies allow them to move quickly underwater. Similar animals are elephants, which are much heavier than hippos and carry swimming equipment with them. Its nose can be used as a breathing tube and can walk underwater for hours.
The strangest thing is that hippos have thick skin, like a layer of armor, three to five centimeters thick, but they are very sensitive to sunlight. In order to protect their sensitive skin, hippopotamus must live in water for more than 16 hours every day, and occasionally cover the skin surface with their own secretions and sludge when they go ashore. Elephants will do similar things. For them, sludge is the best sunscreen, but this habit is not passed on to future generations through DNA, but through learning and imitation. In life, the little hippo will learn how to get into the mud by imitating the actions of his parents to prevent himself from being sunburned by the sun. Without the education of parents, even if the hippo is sunburned, it will not smear its skin with sludge. Therefore, parents are the best teachers for children, which is correct for people and animals.