Perhaps the most significant change is in respiration. As the frog cools, it requires less oxygen. A cooler frog can stay completely submerged for longer periods of time, only surfacing occasionally for a needed gulp of air. With additional cooling, even less oxygen is needed - to the point that all of the oxygen that it needs can be obtained by diffusion through the moist skin. There is little need for blood to go to the lungs, so now much of the blood is sent to the skin. This process, called cutaneous respiration, allows the frog to obtain all the oxygen it requires at low temperatures, and simultaneously remain submerged for extended periods of time. This phenomenon can be observed by looking at the light skin on the belly, which may become pink to reddish with the increase of blood flow. The frog on the right is in hibernation. The skin is reddish due to increased blood flow. Notice also that the arms are outstretched in the "four-point stance."