One of the original Electrodes from Paradise Electro Stimulations, the P.E.S. Acrylic Anal Plugs are constructed out of smooth acrylic rods with a conductive strip on each side to stimulate the anal sphincter muscle and interior of the anal cavity.
These Electrodes begin stimulating before the electricity is even added. The smooth and cleverly contoured sides stretch the sphincter and use the strength of these same muscles to hold the plug securely in place.
(via P.E.S. Acrylic Anal Plugs)