Pegging is a sexual practice in which a woman performs anal sex on a man by penetrating the man anus with a strap-on dildo. Sexual relations between women have been illustrated as well as narrated, but much of the written material from the early modern period has been destroyed. Sexologist Alfred Kind suggested that the buttocks is the primary sexual presentation site in primates. Diaper pornography involves performers wearing diapers, sometimes with an adult performer acting in the role of a caretaker. It has also been recommended as a form of foreplay or safer sex. The concept of lesbian, to differentiate women with a shared sexual orientation, is a 20th-century big tit milf construct. Often, strong views are expressed with regard to anal sex; it is controversial in various cultures, especially with regard to religion, commonly due to prohibitions against anal sex among gay men or teachings about the procreative purpose of sexual activity. Bisexual pornography is a genre of pornography which most typically depicts one woman and two men who all perform sex acts on each other. There may be more than gay fuck two participants; both group sex and gang banging can be included. Most soft crush fetishists avoid being placed under the same label as hard crush fetishists, believing that crush films with larger animals give the entire group a bad label. While anal sex is commonly associated with male homosexuality, research shows that not all gay males engage in anal sex and that it is not uncommon in heterosexual relationships. Participants who exert sexual control over their partners are known as dominants or tops while participants who take the passive, receiving, or obedient role are known as submissives or bottoms. Men may also rub or massage the glans, the rim of the glans, and the frenular delta. Tentacle rape or shokushu goukan is found in some horror or hentai titles, with tentacled creatures having sexual intercourse with female characters. Examples of heterosexual pornographic film series featuring creampies include Cream Filled hentai sex Teens and Internal Cumbustion.