Carl Gustav Hempel's Apple

Origin
Carl Gustav Hempel was a major figure in logical empiricism and the deductive-nomological model of scientific explanation, both commonly used in science during the 1950s and 60s. He is also known for the raven or Hempel’s paradox. As a starting theory, it postulates all ravens are black. By logic, all non-black things are not ravens. But the paradox occurs with the introduction of something like a green apple, supporting the first idea all ravens are black by comparing them to something else.

Effects
Used in a demonstration of Hemp's paradox, observing the apple while it is in the possession of another person makes the observer susceptible to hypnotic suggestion and liable to believe anything the holder tells them. Using it, however, causes complete color blindness in the person who held the apple, and makes nearby birds attack them. The effects stop when the affected beliefs of the observer of the apple are truly believed by someone who was not affected by the apple.