Are you a kid? Does your microwave oven belong to your parents? If so, then don't even THINK about trying any of these experiments.

A fantastic list of RF demonstrations you should never do with your own microwave oven!

If you microwave grapes you can create plasma, and sparks by placing 2 grapes slightly touching each other. (Picture shows the moment it sparks.) I believe this is due to the length of the grape being the same length as the wave-length of the microwave. (Correct me if I'm wrong.)

Great smith chart tool!