In the 1920s, Havelock Ellis reported that turn-of-the-century seamstresses using treadle-operated sewing machines could achieve orgasm by sitting near the edge of their chairs. Often, slave contracts are set out in writing to record the formal consent of the parties to the power exchange, stating their common vision of the relationship dynamic. Scenes of multiple penetration are common in pornography. The term bareback is used less frequently in the heterosexual community. Freud, however, considered porn milf such extensions of sexual interest to fall within the range of the normal, unless marked out by exclusivity . Boot pornography includes hot gay sex women and sometimes men wearing boots for their sexual appeal. Technically this is a form of exhibitionism rather than group sex per se. Fat fetishism also incorporates stuffing and padding, whereas the focus of arousal is on the sensations and properties hentai sex of a real or simulated gain. The effect is to give the viewer the sense that they are experiencing the sex acts that they are watching, as opposed to simply watching others as a voyeur. There are no particular or preferred elements within maiesiophilia that are common to all maiesiophiliacs. There are many other variations on male masturbation techniques. Gang bang pornography is a type of pornography that depicts an individual engaging in physical sexual activity with multiple partners sequentially or at once. Fistees who are more experienced may take two fists . However, that term is usually applied to a male who observes somebody secretly and, generally, not in a public place. A smotherbox has two openings. Simultaneous penetration of the vagina and anus. The term shemale has been used since the mid-19th century, when it was a humorous colloquialism for female, especially an aggressive woman. In a bath or shower a female may direct tap water at her clitoris and vulva. Regardless of its origin, BDSM is used as a catch-all phrase to include a wide range of activities, forms of interpersonal relationships, and distinct subcultures.