Polar bears give off no detectable heat.
A polar bear is so well insulated that it's almost invisible to infrared cameras—except for the space in front of its mouth, where a small cloud of warm breath is the only outward indication of life.
To survive the harsh climates in which they live, polar bears rely on a thick coat of fur on top of a warming layer of fat. Fur even grows on the bottoms of their paws, to protect against cold surfaces but also to give them better grip on the ice. And while their coats are white, to provide camouflage, the skin underneath is black, to better absorb the sun's rays.
Fortunately, not all bears are this stealthy. Otherwise it would be bad news for people on Zoo, who have enough challenges!
Image: John Conrad/Corbis