Prior research on implicit mind-reading skills has focussed on how infants anticipate other persons' actions. This study investigated whether 11- and 17-month-olds spontaneously attribute false beliefs (FB) even to a simple animated geometric shape. Infants were shown a triangle chasing a disk through a tunnel. Using an eye-tracker, we found that 17-month-olds in a change-of-location true belief (TB) task anticipated that the triangle would search for the disk in the correct place while in a FB test they anticipated that it would search for it in the wrong, belief congruent place. These results suggest that 17-month-olds' psychological-reasoning system is applied to the actions of unfamiliar agents and it is employed to anticipate agents' actions even in the absence of any morphological features that are typical of natural agents. These findings provide support for theoretical accounts that emphasize continuity in the development of theory of mind core concepts and belief reasoning skills. (Contains 1 figure.)