
Natural laughter that is pure and has nothing artificial
and also comes from the true and positive feelings,
causes a natural boost of feel good endorphins,
which give us a more optimistic outlook.
On the contrary, the forced laugh that is 
usually rooted in the stressful experiences,
increases the stress hormone levels and 
has negative effects on the others too.
It explains why we love to see  and hear
children laughing.