In individualistic societies, many adolescents go through a solipsistic phase, when they question whether other people really experience the world in the same way as they do. What often seems most in doubt during these musings is whether overt expressions genuinely correspond to deeper private feelings, or whether friends, family, and strangers in particular are simply going through the motions in a more calculated manner. This theme is frequently dramatized in popular books and ﬁlms. For example, the extraterrestrial pod creatures in Invasion of the Body Snatchers are incapable of experiencing emotion but try to inﬁltrate North American society by becoming exact replicas of human beings in all other respects. They look like us, and even act like us in many ways, but something barely perceptible seems to be missing inside.