Preggo pornography features pregnant performers and may include erotic lactation as a fetish. When the interest in a particular subject is obsessive, the behavior may be described as stalking. The cover can have hinges or be a separate part. Some people get sexual pleasure by inserting objects, such as urethral sounds, into the urethra , a practice known as urethral play or sounding. A woman can use a secondary vibrator, gay movies between the dildo and her genitals, to get pleasure from pegging. The niche popularity grew significantly in the latter half of the first decade of the 2000s. Multiple men and women Bisexual pornography features one woman and two men who all perform sex acts on each other. The activity is done by itself or as a part of or prelude to other activities which many times involve sex. Some aspects of the research community distinguish between female ejaculation and what is colloquially known as squirting or gushing. Solo performances in gay pornography have been described in 1985 as either or both active and/or passive , whereas female solo lesbian milfs performances are said to be exclusively passive . Commenting on why there are not as many female macrophiles, psychologist Helen Friedman theorized that because women in most societies already view men as dominant and powerful, there no need for them to fantasize about it. These are often fake. Some masturbate only using pressure applied to the clitoris without direct contact, for example by pressing the palm or ball of the hand against underwear or other clothing. Works in this hentai sex genre may be considered adult for any number of reasons. Some men also enjoy anal stimulation, with fingers or otherwise, without any prostate stimulation. 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. For example, in Australia it is rated Refused Classification . Though there have been numerous gang bang pornographic films since the 1980s, they usually involved no more than half a dozen to a dozen men.