How do posts go viral on Facebook?
It's a question asked (and dubiously answered) by a thousand social media 'gurus' on Twitter every day - but the truth is no one really knows. It's a mix of luck, finding the right audience, and usually just publishing something really cool.
But while we can't know how something goes viral, we can at least see it.
A new series of videos has been made which visualises how content is shared by hundreds of thousands of people on Facebook.
Stamen in San Francisco picked three pictures by George Takei and followed how they "grew" in popularity on Facebook - literally.
"We've tried to capture the frenetic energy surrounding three of the most shared images," the team said.
"Each visualization is made up of a series of branches starting from a single person. As the branch grows, re-shares split off on their own arcs, sometimes spawning a new generation of re-shares, sometimes exploding in a short-lived burst of activity. The two different colors show gender, and each successive generation becomes more and more white as time goes by."
The visualistions were made over a three-month period from July to September.