Works in this genre may be considered adult for any number of reasons. The most common type of erotic spanking is administered on the bare buttocks, but can also be combined with bondage, in order to heighten sexual arousal and feelings of helplessness. It is also known colloquially as gushing or squirting, although these are considered to be different phenomena in some research publications. Patricia Hill 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. The naked appearance of actress Demi Moore in the advanced stage of pregnancy on the cover of Vanity Fair magazine in 1991 marked the beginning of a period which has since seen pregnancy presented by celebrities as a glamorous state of living, while also creating a market for photographers to produce images of pregnant mothers, and for fashion stylists to introduce pregnancy styling to their business. Pornography may fall into more than one gay sex video genre. 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. In S/M, the Sadist is usually the Top and the Masochist the Bottom, but these roles are frequently more complicated or jumbled . Bondage/BDSM Bondage pornography features performers tied up or constrained in various ways. They may regard it as an enhancing momsex element of their sex lives or as their primary form of sexual activity. A homosexual threesome would involve either three men or three women. Threesome can also refer to a love triangle, a three-way romantic relationship. Content featuring male bisexuality has been a growing trend since the advent of internet pornography. Hamedori is a genre of Japanese pornography in which a male adult video actor or director serves as the camera operator. Bear features a combination of middle-aged, hairy gay hentai or overweight males.