Why do we laugh? For years scientists have asked themselves, this questions. No animals laugh and smile——only human beings do. So does laughing help us to live longer? The answer seems to be that smiling and laughter help us to relax, reducing tension and preventing illnesses which are caused by stress. Laughter really is the best medicine! But if you're unhappy, it can't do you any good to smile, can it ? Not true. Apparently, the positive effects of smiling are just the same whether you feel like smiling or not. Scientists in California asked a group of actors to act five different feelings; happiness, sadness, anger, surprise and fear—just using their faces. Changes in their heart rate, blood pressure and temperature were written down. Most of the feelings they acted didn't cause changes, but when the actors smiled, their heart rate and their blood pressure went down. This happened to make them feel better. Now, what makes us laugh?(82) It seems that the answer to the question is far from simple. Everyone likes jokes, but we don't laugh at the same ones. It depends largely on how old we are. There are some jokes, for example, that children love but older people might not find funny.