Animals are diverse, multicellular, living organisms in the Kingdom Animalia. With few exceptions, animals eat organic matter, breathe oxygen, can move, can breed sexually, and secrete waste products. Most animals are vegetarian, although some species are omnivores. Virtually all animals produce a variety of proteins, the building blocks of life. Herbivores eat plants and animal tissues; carnivores eat animal flesh and animal organs such as fur and feathers; parasites have a single celled digestive system and secrete proteins from their anus and intestines; and protists secrete protein from their skin. Humans and other primates are among the Protist species.
Almost all animals have blood cells, which multiply in response to stimuli and provide nutrients to cells occupied by multicellular organisms such as bacteria, yeast, and algae. The major component of blood is red blood cells (RBCs), which are blood-vessels capable of moving through most body fluids and secreting blood products to wherever they are needed. In animals, RBCs are contained in capillaries in the bone marrow, which transport plasma (the major components of blood) and other nutrients to all parts of the body.
The major parts of animals including brain, heart, lungs, muscle, nerves, blood, body fat, reproductive organs, genitalia, gastrointestinal tract, hair, feather, teeth, nails, and fur, constitute the anatomy of the body of animals including humans. All animals including non-human animals share some features in their physiologies and other biologies. In fact, almost everything that animals do is unique, which is why many people feel that animals are spirits or entities having a human characteristic. Spiritual beings include angels, ghosts, demons, and guardian angels, while animal characteristics are such characteristics as self-consciousness, instincts, sexual behavior, language, speech, movement, intelligence, adaptation to circumstances, and personal care.