This is just fascinating:
During experiments on the giant axons of the Longfin Inshore Squid (loligo pealei) at the Marine Biological Laboratory in Woods Hole, MA; we were fascinated by the fast color-changing nature of the squid’s skin. Squids (like many other cephalopods) can quickly control pigmented cells called chromatophores to reflect light. The Longfin Inshore has 3 different chromatophore colors: Brown, Red, and Yellow. Each chromatophore has tiny muscles along the circumference of the cell that can contract to reveal the pigment underneath.
There are some questions as to what is happening and how this works. An iPod plays music by converting digital music to a small current that it sends to tiny magnets in the earbuds. The magnets are connected to cones that vibrate and produce sound.
Since this is the same electrical current that neurons use to communicate, we cut off the ear buds and instead placed the wire into the fin nerve. When the iPod sends bass frequencies (<100Hz) the axons in the nerves have enough charge to fire an action potential. This will in turn cause the muscles in the chromatophores to contract.