Varvoice plankton memorize the sound of human speech and repeat it over and over. They accomplish this amazing feat by oscillating the long flagellum that extends from their heads. By resonating the vibration with their water-droplet-shaped body, the plankton produce sounds that closely resemble the human voice. The body can expand and contract at will. By changing shape, they can easily manipulate the sound of the voice. Words that the Varvoice memorize and play back in reverse have a particularly strange ring to them. Researchers refer to this phenomenon as Varvoice inversion.