While she stands up, he by grabbing her hips enters her from behind For better results as far as sex-rhythm is concerned, she can hold his legs in this sexual-position, and from underneath finger probe his ass, smoothing his testicles alternately. Therein lies the advantage of dual anal-sex with vaginal-sex ( the old in out). Meanwhile, he manually fondles and stimulates her, as in a wall mirror, she sees herself being penetrated.