How can a plant kill?

People kill. Animals kill. Animals and people kill for food, or they kill their enemies. Animals and people can move around and find something to kill. They can run away from an enemy. They can kill it if it is necessary. Many kinds of animals eat plants. They cannot run away from their enemies. Some plants make poison. If an animal eat part of the plant, it get sick or dies. Animals learn to stay away from these plants. There are many kinds of plants that make poison. Most of them grow in the desert or in the tropics. Today farmer use many kinds of poison on their farms. Most of these poison come from petroleum, but petroleum is expensive. Scientists collect poisonous plants and study them. Maybe farmer can use cheap poison from plants instead of expensive poison from petroleum.