Planktonic Noctiluca has a tentacle projected from its cell body (a whip-like projection in the video) . The food organisms are caught at the tip of the tentacle by the mucus covering it. The movements of the food-gathering tentacle is under the control of spontaneously recurring membrane potential changes. The sounds show the membrane potential changes exhibited by the cell of Noctiluca. The higher frequency corresponds to more positive membrane potential. Note that the quick flexion of the tentacle takes place in association with the transient decrease in the frequency (negative shift of the potential; a hyperpolarizing action potential).