These actors often play the top roles but this is not always the case, such as with Kristen Bjorn and some Bel Ami models. Cartoon pornography includes, but is not limited to, hentai and parody renditions of famous cartoons and comics. By comparison, gonzo pornography puts the camera right into the action, often with one or more of the participants both filming and performing sexual acts, without the usual separation between camera and performers seen in conventional porn and cinema. The study also found that participants reacted positively to a much wider range of figures than a control group, even rating emaciated figures higher. Perhaps following the example set by gay pornography, they have become a popular subgenre within heterosexual pornography since the turn of the century, featuring both vaginal and anal ejaculations. Rubber pornography involves rubber, latex, and similar materials. As a form of non-penetrative sex, it can be done for its own enjoyment or as foreplay. A heterosexual threesome may involve two men and a woman, or one man and two women - that is, two men having sex with a woman , or two women with a man. These are often gay cock fake. A facial is a term for the sexual activity in which naked milf a man ejaculates semen onto the face of one or more sexual partners. Medical pornography involves sexualized medical, often fake, including gynecological pelvic examinations, rectal examinations, and pelvic or gynecological hentai movies ultrasounds. Lesbianism in erotica deals with depictions in the visual arts of lesbianism, which is the expression of female-to-female sexuality. Milking pornography features lactating women being milked or milking themselves . Lolita pornography that features actual teenage girls under the age of 18 is illegal in most countries and treated as child or youth pornography. This technique is also used by some men who are circumcised who have excess skin left from circumcision. People may also find masturbating with friends helps lift the stigma naked celebrities they feel surrounding the act.