Pornography may fall into more than one genre. Such ejaculation can be done by mammary intercourse, or masturbation over the other person, or result from the withdrawal of the penis from a partner mouth as he is ejaculating following fellatio, irrumatio, or intercourse. The niche popularity grew significantly gay twinks in the latter half of the first decade of the 2000s. Buttocks are sometimes emphasized in pornography, where they are often referred to as booty. Tentacle erotica can be consensual, but frequently contains elements of non-consensual sex. Both sexes sometimes apply lubricating substances to intensify sensation. The activity is done by itself or as a part of or prelude to other activities which many times involve sex. Though there have been numerous gang bang pornographic films since the 1980s, they usually involved no more than half a dozen to a dozen men. Sadism describes sexual pleasure derived by inflicting pain, degradation, humiliation on another person or causing another person to suffer. Foot fetishism has been defined as a pronounced sexual interest in the feet or footwear. Older names for a pornographic film include stag film, momsex and blue movie. It is geared towards heterosexual men, who most typically define a threesome as such. In Japan, point of view pornography is referred to as hamedori . The term pearl necklace is used by some because the drops of semen deposited by the man resemble a necklace of translucent white pearls. Shotacon : Similar to Lolicon, this genre involves prepubescent or under-aged boys between the ages 6–12. A pornographic work is characterized as hardcore if it has any hardcore content, no matter how small. Double penetration of the vagina, gay hentai anus and mouth, can involve: Simultaneous penetration of the anus by two penises or other objects. Yaoi is anime or manga that features gay males . In general, BDSM play is usually structured such that it is possible for the consenting partner to withdraw his or her consent during a scene; for example, by using a safeword that was agreed on in advance.