Mammals are warm-blooded animals. Mammals bodies always stay the same temperature. Their bodies don't change temperature even if it is freezing cold or burning hot outside.
Mammals can have fur or hair.
Their fur can be any length, size, or style. There may be a lot of hair or just a few stiff hairs. There are only about 4,000 types of mammals, but mammals are chosen most often for pets. Mammals that are most often chosen are dogs, cats, hamsters, guinea pigs, and rabbits. Other common mammals are gerbils and mice.