Doctors think electricity left her body in that spot, and burned her under the skin. After the Flash Once home, Gretel just managed to call 911 before she passed out. Her dogs had been struck too, and had minor cuts and scrapes. It took a few years for Gretel to recover. Even now, five years later, effects of the accident remain.
Static electricity is the key to any kind of lightning.
When negative charges build up in one area, and positive charges build up in another, a beam of electricity may shoot across to even things out. This friction charges the cloud with static. Negative drops fall to the bottom of the cloud, and positive drops rise. The ground takes on a positive charge. Adapted from Scholastic Super Science Blue, March 1996.