The Rock in the Armpit
Before a sea otter dives for a clam, it often tucks a flat stone under its forearm, a pocket it keeps specifically for this purpose. On the surface, it places the stone on its chest, holds the shellfish with both paws, and hammers until the shell cracks. Then it eats, stashes the rock again, and dives for the next one. The same rock. The same otter. Sometimes for days in a row.
