In most people, speech and language live in the brain's left hemisphere. Mora Leeb is not most people. When she was 9 months old, surgeons removed the left side of her brain. Yet at 15, Mora plays soccer, tells jokes, gets her nails done, and, in many ways, lives the life of a typical teenager. I can be described as a glass-half-full girl," she says, pronouncing each word carefully and without inflection. Her slow, cadence-free speech is one sign of a brain that has had to reorganize its language circuits. Yet to a remarkable degree, Mora's right hemisphere has taken on jobs usually done on the left side. It's an extreme version of brain plasticity, the process that allows a brain to modify its connections to adapt to new circumstances. People like Mora represent the upper bounds of human brain plasticity because their brains were radically altered very early in life " a period when the wiring is still a work in progress. During an interview with Mora, both her abilities and deficits were apparent. So was her outgoing personality and curiosity about the world. Mora began by telling me a joke: "How do you make a hot dog stand?" she asks. "You take away its chair." What scientists still want to know is precisely what allowed Mora's brain to rewire so extensively. One thing is clear: Understanding the basis of this sort of extreme plasticity, they say, could help millions of people whose brains are still trying to recover from a stroke, tumor, or traumatic injury. And Mora is helping scientists deepen their understanding, simply by being herself.