"Ha ha," "hee hee," "boo hoo," "waaa, waaa"... the unmistakable sounds of laughing and crying are recognizable all over the world. They're pillars of human communication, yet some researchers say that when it comes to studying human behaviour, there's nothing as poorly understood as laughs and tears. Why did we develop these unusual vocal communication techniques? How uniquely human are these sounds? Meet the neuroscientists, psychology researchers and evolutionary biologists who are exploring every scientific angle of these bizarre and beautiful emotional behaviours.

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