Double penetration of the vagina, anus and mouth, anime hentai can involve: Simultaneous penetration of the anus by two penises or other objects. 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. 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. Sex parties may be organized to enable people to engage in casual sexual activity or for swinging couples or people interested in group sex to meet, but any gathering where sexual activity is anticipated can be called a sex party. A crush fetish is a fetish in which one is sexually aroused usually when someone crushes objects, food, and sometimes small animals with their body, usually under their foot, or when crushed oneself. The arousal from being desperate comes from the sensation of having a full bladder. Sub-genres can also be classified into the characteristics of the performers or the type of sexual activity on which it concentrates, and not necessarily on the market to which each sub-genre appeals. Female ejaculation is the expulsion of fluid by the paraurethral ducts through and around the human female urethra during or before an orgasm. Urolagnia is a form of salirophilia in which sexual excitement is associated with the sight or thought of urine or urination. The term applies to the depiction of the act rather than the act itself, and so does not include live exhibitions like sex shows and striptease. It is used, for example, at fertility clinics to stimulate sperm gay movies donors. 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. The Silent Duck, also called Duck-Billing, is the technique often used in which the person engaging in hand insertion lesbian milfs shapes the hand to resemble a duck beak.