Requirements: P must meet four main requirements to use the doctrine: (1) There must be no direct evidence as to D’s precise conduct; (2) P must show that the harm is of a type that does not normally occur except through the negligence of someone; (3) P must show that the instrumentality which caused the harm was at all times within D’s exclusive control; and (4) P must show that the injury was not due to P’s own negligence.