Have you ever tried to prise apart the shell of a mussel or an oyster? It is practically impossible to do by just pulling, so how does the starfish manage it using only its tiny feet? The secret is that the starfish again uses its feet in relays. It hunches itself over the tightly closed shell and attached its tube feet to either side. By resting some feet and pulling with others the starfish is able to exert a strong pull over a long period, and gradually the bivalve weakens until it gives up the test of strength. Once the valves open a fraction the starfish turns its stomach inside out and pushes it into the shell to digest the contents.