A related term used in the genre is the term naked milf cougar, which implies an older woman as predator. Such works have also often been subject to censorship and other legal restraints to publication, display or possession. Mammary intercourse is known as titty-fucking, titfuck, or a titjob in the United States, as well as tit wank or French fuck in the United Kingdom - the latter term dating back to the 1930s; while a more jocular equivalent is a trip down mammary lane. The resulting consent and understanding is occasionally summarized in 3d hentai a written contract, which is an agreement of what can and cannot take place. Many times a top actor will then be sought as a bottom and the debut is often treated as a notable event or even its own release. Nevertheless, it is only an attempt at phenomenological differentiation. The precise definition of roles and self-identification is a common subject of debate, reflection, and discussion within the community. Studies among BDSM practitioners videos gays in the US have shown that about half of all men find the idea of bondage to be erotic; many women do as well. It is geared towards heterosexual men, who most typically define a threesome as such. When used as an alternative to penile-vaginal penetration, the goal may be to preserve virginity or to prevent pregnancy. Medical pornography involves sexualized medical, often fake, including gynecological pelvic examinations, rectal examinations, and pelvic or gynecological ultrasounds. Point of view pornography is adult entertainment filmed to look as if the watcher were experiencing the sex act themselves. Following World War II, during a period of social repression when governments actively persecuted homosexuals, women developed networks to socialize with and educate each other. Snowballing or snowdropping is the human sexual practice in which one person takes someone else semen into his or her mouth and then passes it to the mouth of the other, usually through kissing. Such grounds and even the definition of pornography have differed in various historical, cultural, and national contexts.