Short answers, pulled from the story.
Anal sex principally means the insertion and thrusting of an erect penis into a person's anus or rectum for sexual pleasure. This definition often serves as the baseline, yet sources note that anal intercourse can sometimes denote only penile-anal penetration while anal sex covers any form of anal activity.
The abundance of nerve endings in the anal region makes anal sex pleasurable for both men and women. In a male receptive partner, being anally penetrated produces a pleasurable sensation when the object rubs against the prostate through the anal wall, while women may find orgasm through indirect stimulation of the clitoris via shared sensory nerves like the pudendal nerve.
A 2010 clinical review by Kimberly R. McBride found that 51% of men and 43% of women had participated in at least one act of oral-anal sex or manual-anal sex. A 2010 study from the National Survey of Sexual Health and Behavior showed that 13% to 15% of men aged 25 to 49 practiced insertive anal intercourse.
Ancient Sumerians had relaxed attitudes toward sex and did not regard anal sex as taboo, while Rome condemned a male citizen taking the passive role in anal intercourse as immodesty. Records show some males in Japan engaged in penetrative anal intercourse with other males, and Moche people of Peru created erotic vases depicting male-female anal intercourse significantly more than any other sex act.