I'm part of an Alzheimer's research tem that aims to end brain disease by engaging the world through online memory tests. This is an ambitious project and we aim for 1 million participants.
Please check us out, www.mindcrowd.org - the test is only 10 minutes and will give you data about how you stack up against others. Send it to your friends, family, etc - With our 1 million strong army we will conduct the largest study of memory and its implications in Alzheimer's and other dementias.
Explanation: This is a Lichtenberg figure. In this case, they are made by bombarding a block of plastic (materials like glass can be used) with an EXTREMELY high voltage, until the plastic traps the electric charge inside. What is seen here is the man releasing the charge from the plastic by giving the electricity a way out of the plastic via the nail on the bar tapped against the plastic. The electricity travels near the speed of light out of the plastic into the nail, and out the grounding wire, in superheated paths, crazing the plastic in the areas it traveled through and leaving the scars you see, as a "tree". Electricity is actually moving out of the block, not in.
It's the same reason why some people struck by lightning have those interesting scars... when they're not having a case of the deaths....