He feels her rump shake as she tries to kick him pulling the strong chains taught. He release her clit for a moment "As soon as you climax I'm going to push my way up to my shoulders. There will be no going back then!"  He returns his attention to her bud licking it rapidly. He just needs her to orgasm. So her walls will relax and pull him deep within her. As he licks her he can feel her chestnut rump quiver in pleasure and her vulva wink against his head. He was so close just a moment more.