For a single revolt to become contagious, Fahmy added, communication is key. In 1848, it was the recently invented telegraph, along with printed newspapers, that clued people in to what was happening across national lines.
Today, it's Facebook, YouTube and Twitter. And when electronic means failed, Egyptian protesters made do the old-fashioned way, with printed instructions about what to do.
At its heart, rebellious contagion feeds off of the sense of inspiration people feel when they see people in similar situations striking back -- and succeeding.
"People see that as a template that they can follow, and they see that it can happen," Fahmy said. "It begins to chip away at that barrier of fear."
What history can't do is help experts predict where revolutions will begin, how far they will spread or how it will all end. Outcomes are often surprising and not always positive. Looking to the past, Fahmy said, is also unlikely to prevent new revolts from cropping up in the future and spreading like the flu.