When two people talk, they don't just fall into physical and aural harmony. They also engage in what is called motor mimicry. If you show people pictures of a smiling face or a frowning face, they'll smile or frown back, although perhaps only in muscular changes so fleeting that they can only be captured with electronic sensors. If I hit my thumb with a hammer, most people watching will grimace: they'll mimic my emotional state. This is what is meant, in the technical sense, by empathy. We imitate each other's emotions as a way of expressing support and caring and, even more basically, as a way of communicating with each other.