The folklore of some Native American tribes told of spirits who lived inside each kernel of popcorn. The spirits were quiet and content to live on their own - but grew angry if their houses were heated. The hotter their homes became,the angrier they'd get - shaking the kernels until the heat was too much. Finally they would burst out of their homes and into the air as a disgruntled puff of steam. Though there are no spirits we know of in popcorn, each kernel of popcorn does contain a small drop of water stored inside a circle of soft starch. (That's why popcorn needs to contain 13.5 percent to 14 percent moisture.) The soft starch is surrounded by the kernel's hard outer surface. As the kernel heats up, the water begins to expand, and pressure builds against the hard starch. Eventually, this hard surface gives way, causing the popcorn to explode. As it explodes, the soft starch inside the popcorn becomes inflated and bursts, turning the kernel inside out. The steam inside the kernel is released, and the popcorn is popped!