In early September, a 14-year-old kid with empty eye sockets strode on stage for a taping of the talk show Ellen. "I'm not blind," he told the host to wild applause, "I just can't see." The story seemed lifted from the pages of a comic book: At the age of 3, Ben Underwood lost his eyes to retinal cancer. Three years later, he discovered that he could sense objects around him by making little clicking noises with his tongue and then listening for the echoes. Now, he uses these clicks to find doorways and locate cars on the street. That's...