First a minor detail: squids do not possess ears. However, the same impulses created when audio is converted to an electrical signal, like what happens inside a microphone, can actually be gently applied to tissue, in this case the dorsal side of a squid fin. Joe Hanson over on It’s OK to be Smart explains this better than I ever will. The video above comes from the team over at Backyard Brains who did some experiments at theMarine Biological Laboratory in Woods Hole, Massachusetts where a squid was hooked up to a special iPod playing Cypress Hill’s 1993 hit Insane in the Brain. Via YouTube:
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.
A number of incredibly smart people even wrote a scholarly paper on the phenomenon aptly titled Neural Control of Tuneable Skin Iridescence in Squid! (via brainpicker)