Cut a large, seedless grape into two halves, taking care not to sever the skin at the join. Lay the grape flat in the middle of a microwave (with the rotating dish removed). You may wish to slice the grape into four for maximum effect. The "skin bridges" act as crazee-ass conductors, so when the microwave is powered up, balls of beautiful plasma will be emitted and will float for a few seconds before being sucked into the microwave's vents. Videotape and post on the internet.