I've left my guinea-pig on the milking machine for an hour or so after his first 'emptying' to allow his balls to refill with more sample fluids. The machine is set on a slow, teasing speed but I can help by applying high-level cock electrics to stimulate him further, and lubrication to step-up the electric effect. He's collared, bound, gagged and milked like a dumb but I can judge the effect of his treatment by the stiffness of his shaft. That tells me it's time to add a metal butt plug with more current and to increase the wanking speed. Will we achieve a second cumming I wonder?