― My 4 and half years old son was often laughed by himself without unusual cause. That's made me wonder, what was happen with his strange attitude? I still didn't get it, why was he acted like that? Sometimes, he laughed loudly, and I must told him to stop laughing. Just like when I tickled his older sister, and he laughed loudly when my daughter threw my hand away. Despite of being as a stress release, what is laugh exactly?Laugh, a complex reflex of the muscles of respiration, face and throat. [...].