During experiments on the axons of the Woods Hole squid (loligo pealei), we tested our stimulus protocol on the squid's chromatophores. The results were both interesting and beautiful. The video is a view through an 8x microscope zoomed in on the dorsal side of the caudal fin of the squid. We used a suction electrode to stimulate the fin nerve. Chromatophores are pigmeted cells that come in 3 colors: Brown, Red, and Yellow. Each chromatophore is lined with up to 16 muscles that contract to reveal their color.
There's a nice explanation of what's going on here: the audio signal is converted to electricity, which stimulates the squid's nerves and causes them to pulse and change color in time to the music (which happens to be Cypress Hill).
more info here