Fig. 6. Velocity vectors from an asynchronous kick based on a ventral view (horizontal light sheet; xz plane) showing the buildup and shedding of the vortex ring generated by the foot. The reference vector equals 1 m s^–1. The four images are separated by 0.04 s. Velocity vectors overlying the foot represent foot movement and illustrate the velocity of the foot relative to the surrounding fluid. Free-stream flow velocity has been subtracted from each vector.