Activate the Temporo-Parietal Junction! A study by UCLA scientists showed that this part of your brain indicates whether you will share something before you know it yourself. (It is also, apparently, responsible for out-of-body-experiences. Which makes total sense in a weird way.)
The TPJ is hooked in big time to empathy, which explains the wonkiest bit about it:
"Three years ago, an MIT team showed that stimulating the TPJ affected moral reasoning: subjects were less likely to care about the inherent morality of a situation (in this case, whether a man should let his girlfriend walk across a rickety bridge) and more about outcomes (did she get across safely?)."
Pretty intriguing to think how this links up with social media sharing -- if I told you this was a link to a bear attack video, would you head on over and watch it? Maybe that's stretching the science a bit, but we have the ability to watch a lot more misadventures online than ever before.
Will people start using these brain studies to make their Youtube videos go viral? I predict yes! Now excuse me, while I tell a few friends about this...