 The reader may recognize the similarity between Einstein’s  exploding gunpowder example  and Schrödinger’s cat (Schrödinger 1935a, p. 812). In the case of the cat an unstable atom is hooked up to a lethal device that, after an hour, is as likely to poison (and kill) the cat as not, depending on whether the atom decays. After an hour the cat is either alive or dead, but the quantum state of the whole atom-poison-cat system at this time is a superposition involving the two possibilities and, just as in the case of the gunpowder, is not a complete description of the situation (life or death) of the cat. The similarity between the gunpowder and the cat is hardly accidental since Schrödinger first produced the cat example in his reply of September 19, 1935 to Einstein’s August 8 gunpowder letter. There Schrödinger says that he has himself constructed “an example very similar to your exploding powder keg”, and proceeds to outline the cat (Fine 1996, pp. 82–83). Although the “cat paradox” is usually cited in connection with the problem of quantum measurement (see the relevant section of the entry on  Philosophical Issues in Quantum Theory)  and treated as a paradox separate from EPR, its origin is here as an argument for incompleteness that avoids the twin assumptions of separability and locality. Schrödinger’s development of “entanglement”, the term he introduced for the correlations that result when quantum systems interact, also began in this correspondence over EPR — along with a treatment of what he called quantum “steering” (Schrödinger 1935a, 1935b; see  Quantum Entanglement and Information).