High-voltage dielectric breakdown within a block of plexiglas creates a beautiful fractal pattern called a <a href="https://en.wikipedia.org/wiki/Lichtenberg_figure" class="extiw" title="en:Lichtenberg figure">Lichtenberg figure</a>. The branching discharges ultimately become hairlike, but are thought to extend down to the molecular level.
Bert Hickman
Attribution
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