Laughing is contagious. A study explains how the brain responds to someone else laughing. When someone else laughs areas light up in the brain of those listening that correspond to the areas that are activated when they are laughing. If we hear someone laughing, we instinctively copy. This is a mirror response that strengthens social bonds. Only laughter produces such a marked effect in our brain. Crying, shouting or screaming also do so but much less than laughing. Researchers have seen that youngsters who are insensitive to the laughter of others are at increased risk of developing psychopathic conditions in adulthood. It is not a question of whether you laugh much or a little, but of whether you are sensitive to the laughter of others. It is not clear if not laughing with others, is a cause or a consequence of the psychopathic risk. Still to be clarified is if this is accompanied by reduced smiling, words of encouragement and shows of affection. Laughing is one of our more spontaneous and early manifestations and one who does not laugh can be easily identified. It is suspected that laughing is a strategy selected by evolution to easily identify those who are at risk of behavioral disorders.