Other tests have shown that laughter appears to be able to reduce the effects of pain on the body.In one experiment doctors produced pain in groups of students who listened to different radio programs. The group that tolerated(忍耐)the pain for the longest time was the group which listened to a funny program.The reason why laughter can reduce pain seems to be that it helps to produce a kind of chemical in the brain which reduces both stress and pain. As a result of these discoveries，some doctors in the United States now hold laughter clinics，in which they help to improve their patients’ condition by encouraging them to laugh.They have found that even if their patients do not really feel like laughing，making them smile is enough to produce beneficial effects similar to those caused by laughter.