Laughter serves weightier purposes than turning noses into milk spigots. More than merely a side-effect of mirth, it acts as a sophisticated social signaling system, helping people bond and even negotiate status. Consider that most social laughter does not result from any obvious joke.
Yukking it up also has numerous health benefits: It lowers anxiety, boosts the immune system, and aids circulation. These contagious convulsions are anything but frivolous.