The author employs neurobiology to help explore deception in nature and self-deception in human beings. She examines activities that may appear playful but that lack such hallmark qualities of play as equality, mutual pleasure, and voluntarism and that can, therefore, prove psychologically destructive. She warns that the kind of playful interactions of parents and children that help connect the concept of self with the concept of other and to expand children's imaginative horizons during healthy development may turn defensive and do harm during severe trauma. Such interactions can shrink mental horizons, help separate mind from body, and facilitate the disconnection of the self from others. These devastating outcomes occur especially when play-like activities seem to offer in fantasy a safety absent from real life. The author uses the clinical case of a victim of sexual abuse to illustrate such unhealthy activity and the compulsion and dissociation it creates, which can foster the epigenetic transmission of incest from one generation to the next.