The document discusses three ways that animals can be classified: by their reproduction as either viviparous (born from the mother's stomach) or oviparous (born from eggs); by their diet as carnivorous (eating animals), herbivorous (eating plants and fruits), or omnivorous (eating plants, fruits, and animals); and by their structure as either vertebrates (having a backbone) or invertebrates (not having a backbone). Examples are provided of different animals' classifications based on these criteria, such as crocodiles being vertebrate, oviparous, and carnivorous.