Sea otters use stones as tools to crack open shellfish resting on their chests.

The longer version

A favourite stone is kept folded in a loose pouch of skin under the foreleg, carried through many dives and retrieved each time. Floating on the back, the animal lays it on the chest and hammers shellfish against it, using a lever action instead of raw jaw strength to open prey that would otherwise resist.

Dense fur traps air for insulation, since these mammals lack thick blubber, so constant grooming and a very high metabolism do much of the warming work. Youngsters pick up the habit by watching their mother and copying her over months. The same learning lets local groups favour whatever prey is most abundant nearby.

Where this entry sits

Oceans and Sea Life looks at the salt water that covers most of the planet, from crashing waves and tides to the darkest deep-sea trenches. Expect notes on coral, fish, whales, sharks, jellyfish, shells, and the strange creatures that live far below the surface. The full list sits on the Oceans and Sea Life page, where every entry is listed in order.