My three young daughters like to watch pets doing silly things. Almost daily, they ask to see animal video clips on my phone and are quickly entertained. But once my 7-year-old lets out a belly laugh, the laughter floodgates are opened and her two sisters double over as well.
This is just what science would predict.
“Laughter is a social phenomenon,” says Sophie Scott, a neuroscientist at University College London who has studied laughter and other human reactions for more than two decades. Scott co-wrote a study showing how the brain responds to the sound of laughter by preparing one’s facial muscles to join in, laying the foundation for laughs to spread from person to person.
“Contagious laughter demonstrates affection and affiliation,” Scott says. “Even being in the presence of people you expect to be funny will prime laughter within you.”