One of the most effective forms of industrial or military sabotage limits itself to damage that can never be thoroughly proven-or even proven at all-to be anything deliberate. It is like an invisible political movement; perhaps it isn't there at all. If a bomb is wired to a car's ignition, then obviously there is an enemy; if public building or a political headquarters is blown up, then there is a political enemy. But if an accident, or a series of accidents, occurs, if equipment merely fails to function, if it appears faulty, especially in a slow fashion, over a period of natural time, with numerous small failures and misfirings-then the victim, whether a person or a party or a country, can never marshal itself to defend itself.