Mexican jumping beans
Mexican jumping beans are a phonemenon native to Mexico where they are known as brincadores.
Physically, they ressemble small tan or brown beans. They are a type of seed in which the egg of a small moth has been laid. It is the moth's larva which makes the "jump". The beans themselves are from a shrub called Sebastiana palmeri or Sebastiana pavoniana, while the moth is of the species Carpocapsa saltitans — "carpo" indicating that it lives within a seed (see podocarp), and "saltitans" referring to its jumping behavior.
After the egg has hatched, the larva eats away the inside of the bean, making a hollow for itself. It attaches itself to the bean with many silken threads. 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 beans are nonetheless far from immobile.
Jumping beans were used as a recurring gag in many cartoons in the 1930s to the 1950s. They are particularly common in the northern desert states of Sonora and Chihuahua; indeed, Álamos, Sonora, claims to be "the jumping bean capital of the world".