Biological anthropologist Helen B. Behind the gay movies Green Door was one of the first pornographic films to feature sex between a white actress with a black actor . Mutual masturbation, mutual manual stimulation of the genitals between partners, can be a substitute for sexual penetration. Rimjob pornography centers around anilingus. 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 . The term BDSM dates back to 1969; however, the origin of the term BDSM is unclear and is believed to have been formed either from joining the term B&D with S&M , or as a compound initialism from B&D, D&S , and S&M. Concerted deployed sexual rejection exercised on the partner can be an aspect of Dominance and Submission as well. These actors often play the top roles but this is not always the case, such nude milfs as with Kristen Bjorn and some Bel Ami models. Cum shots typically do not appear in girl-girl scenes and orgasm is normally implied by utterances, cinematic conventions, or body movement. Works hentai videos in this genre may explore philosophical, political or social issues. Additionally, the buttocks give an indication of the shape and size of the pelvis, which impacts reproductive capability. Spanking can be administered in a number of spanking positions. In humans, females generally have more round and voluptuous buttocks, caused by estrogen that encourages the body to store fat in the buttocks, hips, and thighs. A woman can use a secondary vibrator, between the dildo and her genitals, to get pleasure from pegging. Perhaps following the example set by gay pornography, they have become a popular subgenre within heterosexual pornography since the turn of the century, featuring both vaginal and anal ejaculations. 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.