Reality and voyeur pornography, animated videos, and legally prohibited acts also influence the classification of pornography. Hardcore pornography is pornography that depicts penetration porno gay or extreme fetish acts, or both. In Japanese, the term describes any type of perverse or bizarre sexual desire or act; it does not represent a genre of work. Diaper fetishism, nappy fetishism or diaperism, is a sexual fetish in which a person feels a desire to wear or use diapers. This is commonly called double vaginal penetration or double stuffing. The other person may do the same during or after. Shotacon : Similar to Lolicon, this genre involves prepubescent or under-aged boys between the ages 6–12. Lolita pornography features women who are 18 years old or slightly older, who pretend to be underage teen girls. A bisexual threesome may involve a man having sex with a man and a woman, the woman having sex with a man and a woman, or all three having sex with each other. Interactive pornography, available in CD-ROM and DVD format, allows the viewer to select the particular acts performed at any one time, sometimes with the camera providing a first person view. The cover can have hinges or be a separate part. A scene where many women have sex with one man is referred to as a reverse gang-bang. Many cultures describe pain as an aphrodisiac. For circumcised males, on whom the glans is mostly or completely uncovered, this technique creates more direct contact between the hand and the glans. Additionally, the buttocks give an indication of the shape and size of the pelvis, which impacts reproductive capability. Some people get sexual pleasure by inserting objects, such as urethral sounds, into the urethra , a practice known as urethral play or sounding. These styles are much closer to the style of bondage scenes in mainstream television. Cum shots typically do not appear in girl-girl scenes and orgasm is normally implied by utterances, cinematic conventions, or body movement. The term is typically used by the cinematographer within the narrative framework of a pornographic film, and since the 1970s has become a leitmotif of the hardcore genre.