Why do we laugh?

At first glance, it seems like a very obvious basic human response - we laugh because we find things amusing. But what is it that actually triggers our laughter, do all of us find the same things funny? In the edition of The Why Factor, we also look beyond comedy, at laughter in our everyday lives and the role it plays in the relationships between men and women. We also hear some surprising and disturbing discoveries. Why, for instance, were those who carried out the massacre at Columbine laughing as they shot dead 13 people? (Image: Comedian Omid Djalali. Photo by Thos Robinson/Getty Images)