One way plants fight back is to make poisons. Poisons can warn away enemies by making leaves or fruit taste bitter, or by making the enemy very dizzy or sick. People eat foods with poisons in them every day, but we have learned ways to prepare foods to make them safe. Cassava, an important food for more than 400 million people in tropical countries, contains the poison cyanide. Cassava is a starchy tuber, like a potato.
People usually boil or dry cassava to make it safe.
This takes most of the poison out, but a little is still left. In small amounts the poison in cassava is not harmful. Sometimes poisons in plants can be used to treat sickness, if they are taken in tiny amounts or the plants are prepared a certain way. Scientists think that when people eat cassava every day, the tiny amount of cyanide may actually help protect them against certain diseases, like malaria and sickle cell anemia. For thousands of years people have experimented with plants to find new foods and medicines.