Shawn P. Good wrote:
Ok - here's a strange one. My wife diced up about a quarter of a green
peper this morning and put it in our 10-year-old Hotpoint vented
counter-saver microwave (Model RVM125K003) to soften them before adding them
to an omlette. I heard her scream from the kitchen and ran in to see the
green peppers jumping and sparking, with flames shooting out of the dices.
There were no sparks in the microwave itself - they were only coming from
the vegetables.

===quote===
Dr. Dean and her students, as well as others, have observed that grapes,
carrots, and many other fruits or vegetables, when cut and placed next
to one another and heated in a microwave oven, will spark with
considerable size and duration. There is no ready explanation for this
phenomenon in the physics or chemical literature. There may be a
correlation among the dielectric constant, sample size and shape,
moisture content for different foods, and the amount of sparking that
takes place in the microwave field. In addition, the phenomenon can be
modeled using salt solutions to mimic those present in a typical fruit
or vegetable cell. Anecdotal evidence suggests that a cut edge of the
fruit or vegetable must be present, touching that of another cut edge,
for the phenomenon to occur. This phenomenon seems similar to that of
the 'edge effect' where electrons congregate at the sharp edges and
point of a metal in an electric field and can discharge via a spark to
another edge or point nearby.
===end quote===

http://www.public.coe.edu/department.../research.html