You're sitting on the train home and the person opposite you yawns . Suddenly, you're yawning with him, though you're not tired. This phenomenon confused scientists for years until a recent study found that people tend to sympathize with fellow humans. Supporting this claim was the discovery that those children who were unable to form normal emotional ties with others did not experience contagious  yawning, which showed that humans communicate regularly with out words. Hugo Critchley, a neuroscientist, has conducted an experiment recently, which will prove that happiness and sadness can spread like the common cold. According to Critechley, our mind and body are in constant exchange about how we're feeling. "Emotions are closely linked with states of internal  responses," he explained. " There are also more visible changes in our gestures and facial expression. When we're in a group, these signals can spread to another person. For example, there's the obvious tendency to smile when smiled at and there are less obvious changes that reflect emotions of surprise, anger or sadness such as a change in our heart rate and blood pressure. Hugo Critchley further explained, "Our bodies synchronies and when we like the other person, we ever copy his behavior. Next time you chat with a friend, take note of how you're sitting-- it's pretty likely that you will be the same. Scientists believe it's our way of telling each other that we're partners. Through body language, humans give each other very subtle  but clear signals that show emotions." So, what lessons can we learn from this? " Spend time with happy people-- otherwise your health could suffer," said Critchley." When we're sad, our body goes into fight or flight mode. But when we're happy, our body works normally and we feel relaxed and positive. So we look bright, our skin glows, we feel healthy and it affects everyone around us." From the passage we can learn   _  .
sadness is as contagious as happiness anger is less contagious than friendliness surprise is more contagious than smile surprise is the most contagious among emotions