How do we classify animals?

The document discusses the characteristics of different animal groups including mammals, fish, birds, and reptiles. It describes what they eat, how they breathe, how they reproduce, how they move, and what covers their bodies. Mammals are covered with fur or skin, breathe through lungs, and can be viviparous or oviparous. Fish breathe through gills, move through swimming using fins and tails, and have scales covering their bodies. Birds breathe through lungs, are oviparous, and have feathers covering their bodies. Reptiles breathe through lungs, are oviparous, and move through swimming, slithering, or walking, covered with scales.