As of 2013, little analysis of this paraphilia has been reported in medical literature. Another variant of reality pornography consists of normal couples that are filmed by professionals, in which case the only obvious distinction from amateur pornography is the higher quality of production, filming and editing. A celebrity may allow such a recording to surface willingly, as part of a publicity stunt. Babysitter pornography features usually teenage girls being exploited and having taboo sex with older, male employers. Comic books often featured characters being tied up and tying others up, particularly in damsel in distress plots. Pegging is a sexual practice in which a woman performs anal sex on a man by penetrating the man anus with a strap-on dildo. These scenes may involve the female actor calling for the shot to be directed at some specific part of her body. Going back at least as far as the Christy milf xxx twins in the 1970s, depictions of incest and particularly incest between twins has been a feature of gay pornography. For uncircumcised males, stimulation of the penis in this way comes from the pumping of the foreskin, in which the foreskin is held and slid up and down over the glans, which depending on foreskin length, is completely or partially covered and then uncovered in a rapid motion. Other possibilities are possible, such as a man having sex with two women who are having sex with each other. Mutual masturbation is a sexual act where two or more people stimulate themselves or one another sexually, usually with the hands. Sometimes special furniture is used, such as a queening stool or smotherbox. Hentai is the various forms of Japanese pornography, including H-manga, H-anime, and H-computer games. A somewhat controversial ejaculation control technique is to put pressure on the perineum, about halfway between the scrotum and the anus, just before ejaculating. Can also include auto-fellatio, hentai sex or performing oral sex on oneself. A sub-set of vaginal fisting attempts to photograph the female cervix immediately after the gay boy porn fist is removed from the now-gaping vagina.
