Penguin feet

[Henryn]

How can penguins stand around on the ice for such long periods without their feet freezing?

[homer]

In brief, they have lots of thin blood vessels in their feet and they use these to control the temperature of their blood. They can change how much blood flows through the feet according to whatever the temperature is outside. So they maintain the blood temperature in the feet at a couple of degrees above whatever it is on the ice, (cunning devils) ensuring that the feet don't freeze up.