What observable characteristics can be used as a evidence for classifying a specimen as a animal?

Observable characteristics that can classify a specimen as an animal include the presence of multicellular organization, the ability to move at some stage of life, and heterotrophic nutrition, meaning they obtain energy by consuming other organisms. Additionally, animals typically have specialized cells, such as nerve and muscle cells, and reproduce sexually or asexually. Other distinguishing features may include the presence of a nervous system and complex organ systems.