Who'da thunk that a shark could be warm-bodied, but salmon sharks are. They use networks of blood vessels called retia mirabila -- wonderful nets -- to exchange heat between the blood vessels carrying blood warmed by their muscles and those carrying blood cooled by the sea to keep the eyes, brain, muscles and central body cavity at temperatures as high as 78 degrees Fahrenheit. That's pretty warm for a fish. In fact, salmon sharks have the warmest bodies of all fish. Warm bodies enable fast, powerful and deep swimming. Other fish use retia mirabila in similar ways -- white sharks, tunas and billfish. Some land animals have retia mirabila, too. Giraffes use retia mirabila in their necks to maintain blood pressure when they drop their heads below their chest. Dogs have retia mirabila in their necks and use them as temperature regulators. Penguins have retia mirabila in their noses, feet and flippers. Birds with webbed feet have retia mirabila in their legs.