Yellow, red, and brown chromatophores (organs composed of a large pigment cell) surround a single iridophore, which consists of hundreds of iridescence cells. A nerve bundle (not in view of video) is electrically stimulated when the red square appears in upper left corner. Brief electrical pulses initiate action potentials in the nerves which travel to the iridophores and chromatophores. At first the chromatophores respond, but with time, the iridophores also respond. The movie is 4 times normal speed.