When ducks are paddling in water, above the surface they hardly appear to be doing anything, but under the water, to make every stroke of their webbed feet produce the greatest possible forward thrust, their legs are positioned at the rear of their bodies.
鴨子划水，水面動作不多，水下，為了讓鴨腳每劃一步都產生最大的推力，腳長到了身體後半段，步行時，遂顯得重心失衡，搖搖擺擺。