What is the speaker mainly talking about?

[18]Over time animals have developed many ways to stay away from predators. A predator is an animal that hunts and eats other animals. Hiding is one of the best ways to stay alive. Some animals hide by looking like the places where they live. To see how this works. let’s look at the sea dragon. It is a master of disguise. [19]The sea dragon is covered with skin that looks like leaves. The skin helps the dragon look like a piece of seaweed. A hungry meat eater would stay away from anything that looks like seaweed. Other animals stay safe by showing their colors. They want other animals to see them. Scientists call these bright colors warning colors. You have probably seen animals that have warning colors. Some grasshoppers show off their own bright colors. Those colors don’t just look attractive; they tell their enemies to stay away. Of course, hungry predators sometimes ignore the warning. They still go up to the grasshopper. If that happens, the grasshopper has a backup defense. It makes lots of foam. The foam tastes so bad that the predator won’t do it again. Color doesn’t offer enough protection for some other animals. They have different defenses that help them survive in the wild. [20]Many fish live in groups or schools. That’s because there is safety in numbers. At the first sign of trouble, schooling fish swim as close together as they can get. Then the school of fish makes lots of twists and turns. All that movement makes it hard for predators to see individuals in a large group.