Some scientists have said that pigs wallow in mud because they lack sweat glands and need an alternate way to stay cool. However, one researcher thinks it may be the other way around: maybe they "did not evolve functional sweat glands like other ungulates because they liked wallowing so much." They may have retained the behavior from their water-loving relatives, such as whales. Also, here is an adorable pig who wears rubber boots because she is afraid of mud.