Abstract | The way two people choose to share food reveals how close their relationship is. Very close relationships alleviate the discomfort of exchanging saliva. We measure human inferences about relationships from observed food sharing actions with variable risks of saliva exchange; and then use a formal model of inverse planning to quantitatively capture these inferences. The model that best fits human judgments construes food sharing as a rational communicative social action, according to which actions are chosen both to maximize comfort given a relationship, and to communicate about the relationship itself.
