The human body is affected by electric current (measured in Amperes). If the electric current is strong, it can stop heartbeat and cause death. High current can cause severe burns and even fry the victim alive. In order for current to flow through a body you need a sufficiently high voltage, typically more than 50 volts AC, and the voltage generator must be able to supply enough current. Super high voltages, such as from a small Tesla coil, supply such a small amount of current that a person feels just a tickle. A large Tesla coil can burn and kill. 