Internet celebrities, a reform-minded Saudi prince and a Silicon Valley giant collide.

Open the Snapchat app and zoom out to enter the world map. The usual culprits, like Times Square, Disney World and the Louvre, are covered in red-and-orange blurs, a heat map showing where people are taking the most Snaps. But head over to the Middle East, and you’ll see a blazing-red hot spot for Snapchat enthusiasts — the capital of Saudi Arabia, Riyadh, a gleaming plateau overlooking the Arabian Desert.

The future of medicine? Miniature robots communicating with doctors from inside our bodies.

David Zarrouk carefully places the tiny robot into a cleaned-up pig intestine on his table, and flips on the switch. About the size of a thumb, the miniature robot comes to life and starts worming through the intestine, all the way through the other end. The researcher at Ben-Gurion University in Israel draws his inspiration from the 1960s movie Fantastic Voyage. There, a shrunken submarine swims through a scientist’s bloodstream to repair his brain. Zarrouk hopes to turn what he saw on the screen into reality. “You can call it a gut bot,” he says. He isn’t alone.

Yang Saing Koma wants to make sense of a political situation that some say is not salvageable.

Sitting in a dim office of the Grassroots Democracy Party, behind an “organic” restaurant in Phnom Penh, Yang Saing Koma explains how in 1997, he helped his first farmer. The farmer ascribed to the widespread, yet mistaken, belief that to best grow rice one should plant many rice seeds together and flood the soil. Now Saing Koma is trying to grow a movement from far tougher soil as his party’s candidate for prime minister in Cambodia’s national elections on Sunday.

In honor of the 100th anniversary of Nelson Mandela’s birth, OZY is profiling opposition figures around the globe taking risks in the fight for social justice.