Fig. 2. Top views of a swimming frog during two successive stages of the kick cycle, illustrating the absence of assumed propulsion enhancement mechanisms. (A) Leg extension phase, showing rearward-directed flow around the webbed feet without mutual interference, indicated by the forward-directed flow inbetween (colour indicates flow magnitude, red=v_max 0.66 m s^–1; blue 0 m s^–1). (B) Just after completion of the extension phase showing two separate vortex rings, one from each leg (colour indicates vorticity ranging from –0.15 s^–1=blue to 0.15 s^–1=red).