That last example is a perfect indication of the depth of emotional contagion. Service industry outlets from fast food restaurants to department stores drill into their employees the value and importance of smiling and greeting the customer. We have an all you can eat pizza buffet down here called CiCi’s Pizza that is as well known for the collective greeting of “Welcome to CiCi’s!” each time someone new enters the establishment as they are for their pizza. It doesn’t take the millions of dollars that have been spent in research on the subject to know that people who are engaged in a conversation with someone who smiles tend to smile themselves more often than when engaged in conversation with people who don’t exhibit such positive external attributes. This is true whether the content of the conversation is upbeat or depressing.
What is the point of emotional contagion? For one thing, there is the communicable part of the disease. The physical responses stimulated in listeners it a method for facilitating conversation. Have you ever tried to carry on a conversation with someone who just sits there looking like Donald Trump when he’s been asked to talk about someone other than himself? That deer-in-the-headlights response is not conducive to engaging in long-term conversation.