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. Other objects such as ball point pens and thermometers are sometimes used, although this practice can lead to injury and/or infection. Group sex pornography features at least two men and two women , usually more, who all perform sex acts on each other. A related term used in the genre is the term cougar, which implies an older woman as predator. Sigmund Freud considered foot binding as a form of fetishism. Older names for a pornographic film include stag film, and blue movie. Mammary intercourse is a sex act, performed as foreplay or as non-penetrative sex, that involves the stimulation of the male penis by the female breasts and vice versa. They may be noted for using risqué themes, graphic violence, sexuality or black comedy in a manner that is unsuitable for younger audiences. Works in this genre may be considered adult for any number of reasons. Its gain in prominence has been attributed to its depiction in the film Pecker, which was released in 1998. In POV porn, the shooting style is generally similar to gonzo pornography, with the person receiving sexual gratification holding the camera him or herself—aiming it down at the actress or actor lesbian hentai who is performing nude celebrities the sex act. Femdom features BDSM scenes in which the dominant porn milf partner is female. Transgender pornography features performers who cross-dress for sexual gratification, either for themselves or for their partners. The existence of such content in commercially available pornography is widely considered an urban legend. Solo performances in gay pornography have gay fuck been described in 1985 as either or both active and/or passive , whereas female solo performances are hardcore gay sex said to be exclusively passive . The industry generally refers to such films as adult films, which is part of adult entertainment. Double Stuffed , Double Vaginal , or Double Anal pornography involves the penetration of one orifice by two penises or other objects.