A study of 164 males in Finland from two SM clubs found that 18.2% had engaged in coprophilia; 3% as a sadist, 6.1% as a masochist, and 9.1% as both. 18% of heterosexuals and 17% of homosexuals in the study pool had tried coprophilia, showing no statistically significant difference between heterosexuals and homosexuals. A 2009 study found that heterosexual male fat admirers preferred females that were clinically overweight and rated both overweight videos gays and obese women more positively than slighter individuals. During anal sex, male pleasure can be particularly derived from the prostate, which can lead to an orgasm and ejaculation. Group sex pornography features at least two men and two women , usually more, who all perform sex acts on each other. This is commonly called double vaginal penetration or double stuffing. These styles are much closer to the style of bondage milf fuck scenes in mainstream television. Sadomasochism refers to the aspects of BDSM hentai videos surrounding the exchange of physical or emotional pain. Behind the Green Door was one of the first pornographic films to feature sex between a white actress with a black actor . 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. Among swinging couples, one of the two partners is often the driving force and the other is more passive-supportive of the addition of additional sex parties. In POV porn, the shooting style is generally similar to gonzo pornography, with the person receiving sexual gratification holding the camera him or herself—aiming it down at the actress or actor who is performing the sex act. In the gay pornography industry, which uses amateurs as well as professional actors, the term gay-for-pay refers to actors labeled or believed to be straight but who engage in same-sex sexual activities for money. Mutual masturbation, mutual manual stimulation of the genitals between partners, can be a substitute for sexual penetration.