When people yawn in public, those around them soon start to yawn as well. Roman Atwood from the US demonstrates that yawning is a powerful force just about everywhere. In his video clip, "The World's Most Contagious Prank," he gets yawns from passers-by in countries as far apart as France and Thailand.
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The clip has had more than 3.6 million hits, and makes it clear that yawning can be entertaining as well.