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. Hermaphrodite, also known as herm, refers to pornography, typically hentai, that features persons with the genitalia of both sexes. The existence of such content in commercially available pornography is widely considered an urban legend. John Stagliano is considered to have started the gonzo pornography genre with his Buttman series of films. Lolita pornography features women who are 18 years porno gay old or slightly older, who pretend to be underage teen girls. Pornography in Japan is large and intertwined business of adult entertainment with unique characteristics that readily distinguish it from western pornography. This type of pornography is almost exclusively hentai, as true hermaphroditic humans are not fertile and are not usually found in nature. Men may also rub or massage the glans, the rim of the glans, and the frenular delta. Sigmund Freud considered foot binding as a form of fetishism. Femdom features BDSM scenes in which the dominant partner is female. In some scenes or relationships it may be impossible for consent to be withdrawn in the middle of a scene, or the bottom may have the ability to revoke consent for a relationship as a whole, but not for a particular scene. Use of the agreed safeword is seen by some as an explicit withdrawal of consent. 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. Pornographic films are typically categorized as either softcore or hardcore pornography. Foot fetish pornography features heavy emphasis on the feet of the participants, either in combination with kissing and genital sex or in the context of acts such as trampling or crush fetishism. The niche popularity grew significantly in the latter half of the first decade of the 2000s. Diaper fetishism, nappy fetishism or diaperism, is a sexual fetish in which a person feels a desire to wear or use diapers.