One of the distinctions between a male and female of the mammalian species is that when the male tend to get aroused or are prepared to copulate, they experience a growth of.... oh wait, you're talking about the disc he uses like a skateboard. Originally it was a manhole cover
(.... waits for it......)
but now he has replaced that with a flexible polymer compound that contains of metal fibers and other electro-sensitive elements that hardens
(...waits some more....)
when you run electricity through it. Kind of like the shiny dashboard covers people put on their dashboards to protect from the wear and tear of the sun.