Others such as Dennett have argued that the notion of a philosophical zombie is an incoherent, or unlikely, concept. In particular, nothing proves that an entity (e.g., a computer or robot) which would perfectly mimic human beings, and especially perfectly mimic expressions of feelings (like joy, fear, anger, ...), would not indeed experience them, thus having similar states of consciousness to what a real human would have. It is argued that under physicalism, one must either believe that anyone including oneself might be a zombie, or that no one can be a zombie—following from the assertion that one's own conviction about being (or not being) a zombie is a product of the physical world and is therefore no different from anyone else's.