Researchers know why popcorn kernels burst open, but they’ve long puzzled over the source of the “pop” sound. When popcorn heats up, the moisture inside turns into steam, building up pressure until the hull splits and fluffy white corn bursts out, often as the kernel sails into the air. The pop, slow-motion videos reveal, happens out of sync with the hull’s rupture and the corn’s launch into the air, eliminating two possible explanations for the noise. That left one remaining cause: The sound comes from the release of water vapor as the kernel opens. Learn more here.