Animals are living things that have the following characteristics:
1. Multicellular structure: The body of an animal is composed of multiple cells that are combined in different ways to form tissues and organs.
2. Ability to move autonomously: Most animals can change their position or posture through autonomous movement, and usually have movement organs such as muscles, bones, and joints.
3. Have a nervous system: Animals usually have a nervous system, including a brain and neurons, which enable them to sense changes in the external environment and respond appropriately.
4. Able to take in food: Animals usually need to obtain nutrients from the outside world to provide energy and other necessary substances, and these food sources usually include plants, other animals, or inorganic substances.
5. Have the ability to reproduce: Animals can usually reproduce through sexual or asexual reproduction to produce offspring.
In short, animals are complex biological systems, their life activities are closely connected with the environment, and different types of animals have their own specific physiological and behavioral characteristics.
