Thousands of years ago, people lived only in hot places. They did not live in cold places because they could not keep warm. Then they learned how to make clothes. When an animal was killed, they cut off its skin. They wrapped the skins around their bodies. The skins kept them warm. At first men did not know how to make fire. Sometimes lightning hit a forest and started a fire. Then people took some of this fire to make a fire near their homes. A fire was very important for three reasons. It kept them warm. It also frightened wild animals. They did not attack when they saw a fire. Then another thing was discovered: if you cook food, it tastes much better! But men still did not know how to make fire. When they had a fire, they did not let it stop burning. If it went out, they could not start it again. They had to wait for lightning for a long time to start another fire. Later, they discovered how to make fire. If you rub two pieces of wood together, they become hot and burn. One way of doing it is to make a little hole in a piece of wood. Pieces of wood or dry leaves are put into the hole. You rub the stick between your hands. This makes it turn very quickly. The end in the hole becomes very hot. The small pieces of wood and dry leaves begin to burn. Another way of making fire is to knock two pieces of stone together. This makes a spark (火花). You can use this spark to start a fire. Today we have matches, so we can make a fire when we want to.