For other scenes, particularly in established relationships, a safeword may be agreed to signify a warning rather than explicit withdrawal of consent; and a few choose not to use a safeword at all. Since at least 1973, it has also been used to refer to a sexually attractive young woman. Rough sex pornography is similar to pornography featuring sadomasochism, and typically features a Top who humiliates and/or degrades a Bottom while being physically violent towards them. Targets the male audience, but is much less popular than Yaoi. Examples include the Girls Gone Wild and Girls Who Like Girls Series. A few extremely flexible males can reach and stimulate their penis with their tongue or lips, and so perform autofellatio. For uncircumcised males, stimulation of the penis in this way comes from the pumping of the foreskin, in which the foreskin is held and slid up and down over the glans, which depending on foreskin length, is completely or partially covered and then uncovered in a rapid motion. Pornography is generally classified as either softcore or hardcore pornography. This fetish sometimes originates from childhood memories of needing, or of seeing another needing, hentai porn to urinate. 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 . Although interracial pornography theoretically can apply to depictions of sexual activity between performers of any different racial groups, the term is most commonly used for heterosexual sex acts between black and white performers. English adopts and videos gays uses hentai as a genre of pornography by the commercial mature milfs sale and marketing of explicit works under this label. Most soft crush fetishists avoid being placed under the same label as hard crush fetishists, believing that crush films with larger animals give the entire group a bad label.