Particular areas and processes of the body that change during pregnancy may also become the focus of psychological investment, but nudity or sexual activity is not always essential, and in some cases actual pregnancy is not necessary to invoke arousal. Female dominance refers to BDSM relationships and BDSM scenes in which the dominant partner is female. Throughout history, women have not had the same freedom or independence to pursue homosexual relationships as men, but neither have they met the same harsh punishment as homosexual men in some societies. Women who perform in lesbian pornography often do not consider themselves lesbian or bisexual. 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. Some may keep their hand stationary while pumping into it with pelvic thrusts in order to simulate the motions of sexual intercourse. John Stagliano is considered to have started the gonzo pornography genre with his Buttman series of films. It contains graphic hentai movies sexual activity and visible penetration. Terminology for roles naked milf varies widely within the various BDSM subcultures. Its gain in prominence has been attributed gay bear porn to its depiction in the film Pecker, which was released in 1998. Arcane or occult pornography involves sexualized situations with an occult or magical tone or performers who costume themselves in keeping with the theme, for example, a male performer dressed as a wizard. Starting with erotic stories and woodblock prints from before the 20th century, Japanese pornography evolved into distinct subcategories with the media that in addition of pornographic videos and magazines featuring live actors, there is exist categories of pornographic manga , pornographic computer games , and pornographic anime . Transgender pornography features performers who cross-dress for sexual gratification, either for themselves or for their partners. The term sadomasochism is derived from the words sadism and masochism .