Many a careless cook has witnessed this startling phenomenon. Collier N. Smith of the National Institute of Standards and Technology in Boulder, Colo., explains:

"Good conductors, such as metal objects, act like antennas to pick up the intense electromagnetic field generated in microwave ovens for the purpose of heating food. This process can induce a large electric voltage in the conductor, which then can arc to the wall of the oven or to other conductive objects in the oven, thereby creating the observed sparks