An animal is a living creature that can move around on its own, eats food for energy, and responds to the world around it. Animals include everything from tiny ants and colorful butterflies to enormous elephants and whales. Unlike plants, which make their own food from sunlight, animals must find and consume their food, whether that means a lion hunting a gazelle, a hummingbird sipping nectar, or you eating a sandwich.

Scientists have identified over a million different animal species, and they estimate millions more haven't been discovered yet. Animals live everywhere on Earth: in oceans, forests, deserts, and even in frozen Antarctica. Some animals, like dogs and cats, live with humans as pets. Others, like tigers and eagles, live wild and free.

What makes something an animal? All animals are made of many cells (unlike bacteria), they can move at some point in their lives (even coral, which looks like a plant, starts life swimming), and they have senses that help them experience their environment. Humans are animals too, though we often use the word animal to mean creatures other than people. When someone acts wildly or rudely, people might say they're behaving “like an animal,” though this isn't really fair to animals, many of which show remarkable gentleness, intelligence, and devotion to their families.