In the wild, the sense of smell fulfils animals basic needs, like the search for food. A hungry polar bear living in a barren and frozen landscape can smell the carcass of a seal over great distances, and it can also tell from the smell whether the carcass is going to be fit to eat or not.
Animals that live on land receive scent messages through the air, but scents can be detected in water too. Sharks have a highly efficient sense of smell, and the hammerhead shark has evolved its strange shaped head in order to make it an even more efficient hunter. The hammerhead can detect blood at several hundred meters. It has nostrils at each end of its T-shaped head, and by moving its head from side to side it can home in on its prey, by following the stronger of the two scent signals.