If you want to melt the Internet, best to traffic in emotion, researchers have found. The emotional response can be happy or sad, but the more intense it is, the more likely the story is to be passed along.

In a study led by Rosanna Guadagno, a social psychologist at the University of Texas at Dallas, 256 participants much preferred to forward a funny video than one of a man treating his own spider bite. But they were likely to share any video that evoked an intense emotional response, Dr. Guadagno found.

Similarly, Jonah Berger and Katherine Milkman, professors at the Wharton School at the University of Pennsylvania, have found that uplifting articles are more likely than disheartening ones to land on the most-emailed list at The New York Times. But even stories evoking rage or other negative, strong emotions are emailed by readers more often than ones that are simply depressing.