Cut a grape in half, leaving the hemispheres attached by an isthmus of skin. Then irradiate the pair in a household microwave oven. Those are the directions for a deceptively simple experiment Patrick Michaud published online in 1994. Within a few seconds, sparks emanate from the skin bridge and ignite a plasma. For decades the popular parlor trick has delighted and surprised millions of YouTube viewers, science-fair participants, and others, including readers of this magazine (see Back Scatter, Physics Today, October 2017, page 96). In my lab at Trent University the oddity has blossomed into a research project involving several undergraduates, many pounds of charred fruit, and a dozen broken microwave ovens.

This past year we published our own account of the phenomenon. To some people the surprise comes from seeing biological tissue spark in ways they have come to expect only from metallic objects. But to us...

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