Humans understand mechanical events to involve physical bodies interacting by contact, but intentional events involve agents that can also interact at a distance. We investigated infant sensitivity to causality in a simple event in which one agent appears to react to another without contact. Infants 9 months old were habituated to one of two events involving a computer-animated red square moving nonrigidly--like a caterpillar--towards a green square. In the 'reaction event', the green object moved in turn before the red one stopped, while in the 'pause event' the green object moved after the red one stopped. After habituation, each infant saw the habituation movie played in reverse. This test involved identical spatiotemporal changes for reaction and pause event, but the reversed reaction additionally involved a change in the causal roles. Infants dishabituated to reversal of the reaction but not the pause event, a result which suggests sensitivity to causation-at-a-distance. This ability could support development of social cognition and theory of mind.