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. Some pornographic films use an artificial semen substitute to simulate or enhance creampie shots. Use of the agreed safeword is seen by some as an explicit withdrawal of consent. Other objects such as ball point pens and thermometers are sometimes used, although this practice can lead to injury and/or infection. Examples of mentally oriented practices are education games, during which the dominant requires certain forms of behavior from the submissive. Men may also rub or massage the glans, the rim of the glans, and the horny milfs frenular delta. It is typically animated pornography, as the legal age to hentai movies be featured in a pornographic film in Japan is 18. Preggo pornography features pregnant performers and may include erotic lactation as a fetish. The term sadomasochism is derived from the words sadism and masochism . Works in this genre may explore gay bear porn philosophical, political or social issues. The glans itself may widen and lengthen as the stimulation continues, becoming slightly darker in colour, while the gliding action of the foreskin reduces friction. Solo performances in gay pornography have been described in 1985 as either or both active and/or passive , whereas female solo performances are said to be exclusively passive . A scene where many women have sex with one man is referred to as a reverse gang-bang. Portrayals of lesbians in the media suggest that society at large has been simultaneously intrigued and threatened by women who challenge feminine gender roles, and fascinated and appalled with women who are romantically involved with other women. Common phrases used to refer to these individuals are chicks with dicks or the derogatory term shemale, although these are generally considered pejorative among transwomen. In Japan, point of view pornography is referred to as hamedori . Femdom features BDSM scenes in which the dominant partner is female.