Sea anemones use their tentacles to catch food. The sting capsule or nematocyst, in the tentacles contains a coiled, hollow filament that is usually barbed and contains poison. When triggered by touch or chemical stimulus, the internal fluid pressure in the stinging cells increases rapidly and forces the thread-like filament to shoot out.
These barbed threads pierce the skin of the sea creature and inject poison. The anemone moves all the nearby tentacles around the creture to hold and sting it before moving the creature towards the mouth.