For much of the history of cinema and television, lesbianism was considered taboo, though since the 1960s it has increasingly become a genre in its own right. Oral sex pornography frequently features a person big tit milf performing fellatio, and less frequently cunnilingus. The existence of such content in commercially available pornography is widely considered an urban legend. Point of view pornography is adult entertainment filmed to look as if the watcher were experiencing the sex act themselves. Pornographic films are typically categorized as either softcore or hardcore pornography. When used as an alternative to penile-vaginal penetration, the goal may be to preserve virginity or to prevent pregnancy. Contrary to the other two types, B/D does not define the Tops and Bottoms itself, and is used to describe the general activities with either partner being the receiver and the giver. In POV porn, the shooting style is generally similar to gonzo pornography, with the person receiving sexual gratification holding the camera him or herself—aiming it down at the actress or actor who is performing the sex act. Both sexes sometimes apply lubricating substances to intensify sensation. Diaper fetishism, nappy fetishism or diaperism, is a sexual fetish in which a person feels a desire to wear or use diapers. At the end of the evening the female partners would randomly select keys from the bowl and leave with that key owner. The strategies and tactics that are used to smuggle gay twinks one of the couple into and out of the toilet undetected are as important or almost as important as the urination. Evolutionary psychologists suggest that rounded hentai sex buttocks may have evolved to be desirable trait because they provide a visual indication of the woman youth and fertility. A related term used in the genre is the term cougar, which implies an older woman as predator. The warm sensation felt when urine trickles on the body seems to give very relaxing and pleasurable feelings to the person. Masturbation is the self-sexual stimulation of the genitals for sexual arousal or other sexual pleasure, usually to the point of orgasm.