Damn, that's really cool. My concern with doing this with more than a demo setup would be elecrolysis injury due to long-term exposure to direct current. Human

Damn, that's really cool. My concern with doing this with more than a demo setup would be elecrolysis injury due to long-term exposure to direct current. Humans are basically big bags of electrolyte solution, so applying DC for long periods of time results in ions bunching up at the electrodes and all sorts of nasty chemical effects. This is the main danger when children inadvertantly swallow coin cell batteries: it's not actually the heat that causes GI damage (heat generation from a shorted coin cell is minimal), it's the electrolysis-induced chemical burns that result when the battery pumps a few tens of mA through GI tissue. Is it possible to achieve the same effect using an AC waveform? That would likely be safer since it won't result in polarization. EDIT: also, I wouldn't do this to myself, at least not with a 9V battery and a couple of pieces of aluminum foil...