“If we think about emotion this way-as outside-in, not inside-out-it is possible to understand how some people can have an enormous amount of influence over others. Some of us, after all, are very good at expressing emotions and feelings,which means that we are far more emotionally contagious than the rest of us. Psychologists call these people "senders." Senders have special personalities. They are also physiologically different. Scientists who have studied faces, for example, report that there are huge differences among people in the location of facial muscles, in their form, and also-surprisingly-even in their prevalence. "It is a situation not unlike in medicine," says Cacioppo. "There are carriers, people who are very expressive, and there are people who are especially susceptible. It's not that emotional contagion is a disease. But the mechanism is the same.”