Jerk off instruction features a performer encouraging or instructing the viewer to masturbate, often culminating in a countdown at the end of which the viewer is invited to induce orgasm. It is commonly depicted in pornography, but very rarely in mainstream cinema. Gay-for-pay describes male or female actors, pornographic stars, or sex workers who self-identify as heterosexual but who are paid to act or perform as homosexual professionally. This style of filming is in contrast to having a separate, third-person camera crew filming all the action. Bhabha, Anne McClintock and Kobena Mercer. Voyeurism: Seeing another urinate without the person knowledge either through video taping by a hidden camera, or by lurking in locations where people are urinating or are likely to have an urge to urinate. The anus has a relatively high concentration of nerve endings and can be an erogenous zone, and the receiver may receive pleasure from external anal stimulation. Especially popular in post-World War 2 gay video Japanese culture. Pornography may be presented in a variety of media, including books, magazines, postcards, photographs, sculpture, drawing, painting, animation, sound recording, film, video, and video games. The person receiving anilingus is regarded as the passive partner in the act, and the person performing anilingus is the active partner. The term soft crush refers to the more common fetish surrounding videos involving inanimate objects or small invertebrates being crushed, while the term hard crush refers to such videos involving larger animals with vertabrae, and arguably more pain-susceptible animals . Sexologist Alfred Kind suggested that the buttocks is the primary sexual presentation site in primates. They further argue that setting a discrete line between safe and not-safe activities ideologically denies consenting adults the right to evaluate risks vs rewards for themselves; that some adults will be drawn to certain activities regardless of the risk; and that BDSM play—particularly higher-risk play or edgeplay—should be treated with the same regard as extreme sports, with both respect and the demand that practitioners educate themselves and practice the higher-risk activities to decrease risk.