Particular areas and processes of the body that change during pregnancy may also become the focus of psychological investment, but nudity or sexual activity is not always essential, and in some cases actual pregnancy is not necessary to invoke arousal. This type of pornography is almost exclusively hentai, as true hermaphroditic humans are not fertile and are not usually found in nature. Those with diaper-related paraphilias differ widely in their focus of attention. What seems clear from the historical record is that much of the lesbian material in pornographic texts was intended for a male readership. Internationally, hentai is a catch-all term to describe a genre of anime and manga pornography. Medical pornography involves sexualized medical, often fake, including gynecological pelvic examinations, rectal examinations, and pelvic or gynecological ultrasounds. Sexual orientation Pornography features an increasing variety of combinations of actors by their sexual orientation such as lesbian, gay, bisexual, and transsexuals in addition to traditional heterosexual roles. Sadism describes sexual pleasure derived by inflicting pain, degradation, humiliation on another person or causing another person to suffer. This makes varying degrees of stimulation an integral part of oral sex for many men. Pornography is often distinguished from erotica, which consists of the portrayal of sexuality with high-art aspirations, focusing also on feelings and emotions, while pornography involves the depiction of acts in a sensational manner, with the entire focus on the physical act, so as to arouse quick intense reactions. Is also common gay sex video of the furry genre. Bear features a combination of middle-aged, hairy or overweight males. The most common male masturbation technique is simply to hold the penis with a loose fist and then to move the horny milfs hand up and down the shaft. Group sex most commonly takes place in a private sex party or semi-public swinger gathering, but may also take place at massage parlors or brothels or, in some 3d hentai jurisdictions, at purpose-built locations such as sex clubs.