A ringed seal swims about under the sea ice of the Arctic Ocean. In order to survive, the seal must keep open a breathing hole. Regular work with teeth and claws creates a small opening to the surface. However, with their acute sense of smell, polar bears can detect these breathing holes. A polar bear sniffs around on the surface of the pack ice and digs at the snow, then lies down beside it. The bears often wait to pounce on a seal when it comes up for air, but the seal can detect any vibration the bear makes. The seal therefore swims away to an alternative breathing hole.