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To explore the difference between Quantum Bayesianism and the standard interpretation of quantum mechanics, consider the famous example of Schrödinger's cat. In the standard telling, a cat and a vial of poison are sealed in a box. A quantum event that happens with a probability of 50 percent breaks (or does not break) the vial and kills (or does not kill) the cat. Before an observer looks inside the box, the wave function describing the system is in a superposition of both “alive” and “dead” states, as is the cat itself. The observation collapses the cat into one state or another. In QBism, by contrast, the wave function is merely a description of the observer's mental state. The superposition applies to this state, nothing more. The cat is either alive or dead; the observation reveals which.