How do you explain to people that they are a YouTube sensation, when they have never heard of YouTube or the Internet? That's a question we faced during our January visit to North Korea, when we attempted to engage with the Pyongyang traffic police. You may have seen videos on the Web of the capital city's "traffic cops," whose ballerina-like street rituals, featured in government propaganda videos, have made them famous online. The men and women themselves, however—like most North Koreans—have never seen a Web page, used a desktop computer, or held a tablet or smartphone. They have never even heard of Google...