Abstract: Self-propelled aquatic toys lide toy sharks are known having a body portion, a middle tail and an outer tail. The middle tail has been driven to oscillate from side to side while outer tail has flapped freely from side to side. Better propulsion and simulation is, however, achieved by driving the outer tail. In this way, operation of the drive at either limit of oscillation initially drives the outer tail to the same sense, i.e. left or right, as the middle tail and thereafter the middle tail and together with the outer tail is moved from that limit position towards the other limit position.