is an occurrence native to Mexico, where it is known as Frijoles saltarines . Physically, Mexican jumping beans resemble small tan to brown beans. They are a seed pod through which the larva of a small moth has chewed. The bean "jumps" because when it gets in a hot place the larva snaps its body hoping to roll to a cooler place. The beans themselves are from a shrub of the genus Sebastiania, itself often referred to as the jumping bean, while the Jumping Bean Moth is a member of the large genus Cydia.
When the bean is abruptly warmed, for instance by being held in the palm of the hand, the larva twitches and spasms, pulling on the threads and causing the characteristic hop. "Jump" is often an exaggeration, but the bean does noticeably move around.
To rehydrate the beans, they need to be soaked, not submerged, for a three-hour period in chlorine-free water once or twice a month. The chlorine found in tap water in some locales will kill them.