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. 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. The queening stool is also related to a smotherbox, which also allows the person under the seat to be locked in place, restrained by the neck as in a set of stocks. 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. Most bisexual porn is made by small production companies rather than the major studios. The term has also applied to other professions and gay movies even companies trying to appeal to a gay demographic. Breast fetishism is a paraphilic sexual interest focused momsex on female breasts . 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. If one person is penetrated by two objects, it is generically called double penetration . Older names for a pornographic film include stag film, and blue movie. 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. Other fetish Bareback pornography features performers who are not wearing condoms. Internal lesbian hentai ejaculation shots are a comparatively recent development in pornography; they are not found in early pornographic films. Reality and voyeur pornography, animated videos, and legally prohibited acts also influence the classification of pornography.