Clothed male, naked female is one-sided female nudity in which one or more females are nude while one or more men are clothed. Patricia Hill Collins, an African-American writer, theorizes that this is derived from a stereotype that those of gaysex black descent are promiscuous, and their buttocks are objectified by porn as a result. Tentacle erotica can be consensual, but frequently contains elements of non-consensual sex. It is used, for example, at fertility clinics to stimulate sperm donors. The cover can have hinges or be a separate part. Bondage pornography specializes in the depiction of sexual bondage or BDSM activities as photographs, stories, movies, or drawings. A woman can use a secondary vibrator, between the dildo and her genitals, to get pleasure from pegging. Most bisexual porn is made by small production companies rather than the major studios. The niche popularity grew significantly in the latter half of the first decade of the 2000s. Both sexes sometimes apply lubricating substances to intensify sensation. This can, however, redirect hentai sex semen into the bladder . The Silent Duck, also called Duck-Billing, is the technique often used in which the person engaging in hand insertion shapes the hand to resemble a duck beak. They may regard it as an enhancing element of their sex lives or as their primary form of sexual activity. Two women tapegagged and cuffed to iron bars Bondage and Discipline are two aspects of BDSM that do not seem to relate to each other because of the type of activities involved, but they have conceptual similarities, and that is why they appear jointly. The volume of semen that is ejaculated depends on several factors, including the male health, age, degree of sexual excitement, and the time since his last ejaculation. Both forms of pornography generally contains nudity. 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 milf xxx or bottoms.