One obvious difference between plants and animals is that animals move about. The main reason for this is that animals need to search for food, whereas plants can make it themselves. Most plants remain in one position all their lives, and take their food from nature. The main ingredients are carbon dioxíde, water, and mineral salts from the soil. With the aid of sunlight and a green plant substance called chlorophyll, they manufacture their own foodstuffs. These are the sugars, starches, fats and proteins. Animals have no chlorophyll, so cannot do this. Instead they must eat the plants, or one another if they are hunters, in order to live. Animals have to find food, and avoid being caught to provide food for others. They search for a mate and protect their young. They must be aware of their surroundings and know what is happening around them. This is why they have a brain and a nervous system.
The study of animal behavior, called ethology, is an attempt to find out how and why animals behave in the way they do. Since earliest times we humans have hunted animals, and have needed to know their habits and movements. A trained naturalist or hunter is experienced in this, but when it comes to understanding why they act in different ways, this is not always easy. This is because we are also animals, and sometimes make the mistake of thinking that animals behave in the same way as we do. For example, a dog sits up and opens its mouth as if it were laughing. But is this really so? We often compare ourselves to animals by using such expressions as cheeky monkey, greedy pig, vain peacock, sly fox and wise owl, when people seem to behave like them. Actually a monkey is behaving like a monkey, and a pig like a pig. In fact the animals are simply being themselves. This is their natural way, and has nothing to do with us.
