In the everyday business of interpersonal interaction, faces do a lot of the important work. As well as carrying their own speciﬁc meanings, they set the tone for whatever else is happening, ironizing the surface content of a sentence or drawing attention to hidden semantic subtleties. A criticism delivered with a smile or wink, for example, has a quite different effect from one accompanied by scowls. Being face-to-face also makes obvious and inescapable differences to how we engage with one another. Catching someone’s eye is often a prerequisite to starting a conversation, and the course of the ensuing dialogue is directed and redirected by the exchange of looks, yawns, and grimaces. As we interact, we seem to be acutely responsive to the slightest twitch or contraction of facial muscle.