He knows it and that's wny he enjoys it so much. That, and because it feels amazing.

So he laughs and gives it faster, feeling every wet thrust send tendrils of hot pleasure through his centre, coiling at the base of his balls. And he stops the idle fingering; he pushes his thumb and forefinger together, holds them still so that every time she moves back her hard clit will slide between the groove he's made for it. He wants to push her along, wants to see if he can make her come on him before he lets go.