tldr; Adults and children in Germany and Ecuador can distinguish between different types of interactions (chasing, playing, fighting, courting) from motion cues (aka mouse movements) alone. Abstract: One of our most fundamental cognitive adaptations is the ability to infer the intentions of others. Whole-body motion is a reliable, valid, easily perceived source of information about intentions because different kinds of intentional action have different motion signatures. In this study, we report four experiments that examined the ability of German adults, German children, and Shuar adults from Amazonian Ecuador to distinguish, on the basis of motion cues alone, between six categories of intentional interaction: chasing, fighting, courting, following, guarding, and playing. Naturalistic motion trajectories were elicited from untutored participants in a game-like situation with performance- based monetary payoffs and were categorized by other participants in a forced-choice design. On a six- category task, German adults correctly categorized intention 75% of the time (where 17% represents chance performance). On a four-category judgment task, children’s performance was above chance by age 4, with a mean of 64% correct. A final study compared the judgments of German adults with those of Shuar hunter-horticulturalists. Performance was identical and well above chance in both populations, suggesting that cognitive adaptations for inferring intention from motion deserve further research as possible universal components of human psychology.