It is dangerous because it fools people into thinking the lightning danger is gone because the storm is not overhead. The long bolt that strikes to the left of the storm cloud is an example of anvil lightning. Large electric current flowing through air, visible as an intensely bright, hot light.
Arcs are similar to lightning in that the current flows through a channel of ionized air.
A rare phenomenon described as a floating, illuminated sphere that occurs during thunderstorms. It may move fast, slow or stay stationary, it may be quiet or produce a hissing or crackling noise, it may pass through windows, last from seconds to minutes, and disappear slowly or suddenly either quietly or with a loud bang. No definitive photographs have ever been obtained of ball lightning, nor have any official accounts been made of it, therefore its existence is questionable. The illuminated parts of the stepped leader that are not part of the main channel. They are only visible during the first return stroke, and are somewhat dimmer than the main channel.