A facial is a form of non-penetrative sex, though it is generally performed after some other means of sexual stimulation, such as vaginal sex, anal sex, oral sex or masturbation. Sexologist Alfred Kind suggested that the buttocks is the primary sexual presentation site in primates. The buttocks in human females thus contain more adipose tissue than in males, especially after puberty. The term lesbian is also used with regard to sexual identity or sexual behavior, regardless of sexual orientation, or as an adjective to characterize or associate nouns lesbian hentai with female homosexuality or same-sex attraction. First found in softcore movies and erotic thrillers, depictions of big tit milf lesbianism entered mainstream cinema in the 1980s. In addition to mainstream pornography, the popularity of facials has led to creation of its own niche market, like video series that specialize in showing the act. In human sexuality, a threesome is sexual activity that involves three people at the same time. Examples include the Girls Gone Wild and Girls Who Like Girls Series. Enema pornography involves adults given enemas to others, often fake. Depictions of male and female masturbation are common in pornography, including gay pornography. Kinbaku means tight binding Kinbaku-bi which literally means the beauty of tight binding. Omorashi: The act of holding one own urine until the need to urinate is urgent, making another hold in their urine, or watching another person with an urgent need to urinate. Guro or Gore is a genre of Japanese pornography involving blood, gore, disfiguration, violence, mutilation, urine, enemas, or feces. Lucky Pierre is slang for a person performing both receptive and insertive anal and/or vaginal sex simultaneously during a threesome, being positioned between the two partners. Others videos gays involve partners who naturally have a significant difference in size. Such films continued to be produced but could only be distributed by underground channels. In the context of consensual erotic activities, sadism and masochism are not strictly accurate terms; there is a significant difference from the medical or psychological usage of both terms.