There is a clam in the East Sea that, when hungry, swims to the shore, opens its two shells, and from within crawls out a tiny crab, tethered to the clam by a red thread.

The little crab swims about within a few feet of the clam, hunting automatically, and upon being sated, it retreats back into the shell.

Should someone dive beneath the water and sever that red thread, the clam and the crab will both inevitably perish.