In 1777, German physicist Georg Lichtenberg made a curious discovery: when dust in the air settled on electrically charged plates, beautiful tree-like figures formed. The so-called Lichtenberg ‘dust figures’ are branching patterns that are created when high voltage discharge passes either along a surface or through insulating materials.
Interestingly, these branching patterns are also seen on the skin of people who have been struck by lightning. The awesome video above shows what the branching pattern looks like when scientists trap lightning in a box, where you can see the fractal pattern that lightning makes.
Wikipedia has extensive information on the history and science of these fascinating fractal figures here.