Such celebrity news grounds and even the definition of pornography have differed in various historical, cultural, and national gaysex contexts. These actors often play the top roles but this is not always the case, such as with Kristen Bjorn and some Bel Ami models. The activity is done by itself or as a part of or prelude to other activities which many times involve sex. Yaoi is anime or manga that features gay males . Some people get sexual pleasure by inserting objects, such as urethral sounds, into the urethra , a practice known as urethral play or gaysex sounding. Erotic spankings are commonly combined with other forms of sexual foreplay. Swinging can take place in various contexts, ranging from a spontaneous sexual activity at an informal social gathering of friends to a regular social gathering in a sex club or residence. A scene where many women have sex with one man is referred to as a reverse gang-bang. Women with women Main article: Lesbianism in erotica: Lesbianism in contemporary pornography Lesbian or girl-girl pornography features women engaged in sex together, but is typically aimed at a male audience. Testosterone discourages fat storage in these areas. There are various subcultures under this umbrella term and distinct difference between these subcultures. See also Gay-for-pay. Being forced to wear diapers as a form of humiliation is sometimes a behavior encountered in sexual masochism. Female masturbation involves the stroking or rubbing horny milfs of a woman vulva, especially naked celebrities her clitoris, with an index or middle hentai sex fingers, or both. However, various groups within society considered such depictions immoral, labelling them pornographic, and attempting to have them suppressed under obscenity laws, with varying degrees of success. Works in this genre may be considered adult for any number of reasons. Patricia Hill mobile porn tubes Collins, an African-American writer, theorizes that this is derived from a stereotype that those of black descent are promiscuous, and their buttocks are objectified by porn as a result.