Researchers at Wake Forest University had 25 volunteers watch a five minute video of a person either scratching their arm or sitting idly. As the videos played, the volunteers who were viewing the images of scratching were twice as likely to start scratching, as well. (Admit it: You totally want to scratch your arm as you're reading this.)

Our impulse to mimic the itching of others may have evolved as a way to prevent parasitic infestations from jumping from person to person, suggest the researchers.