Enema pornography involves adults given enemas to others, often fake. Actors are mostly amateur; any well-known actors in bisexual porn tend to be from the gay pornography industry. Gang bang pornography is a type of pornography that depicts an individual engaging in physical sexual activity with multiple partners sequentially or at once. It can be combined with fellatio and the woman may move her breasts up and down on the penis for an additional stimulation, usually before the man reaches orgasm. Partners can engage in penetrative sex, known as full swap, or choose to soft swap in which they engage only in non-penetrative sex. In many cases, that person is also aroused by smelling body parts that have a urine scent. Cum-shot pornography features a collection of male ejaculation scenes. Sometimes, hot gay sex asymmetric and often intentionally uncomfortable positions are employed to heighten the psychological impact of the bondage. It may also involve touching, rubbing, or pinching the nipples or other erogenous zones while masturbating. Shemale is a term primarily used in sex work to describe a trans woman with male genitalia combined with female secondary sex characteristics, usually including augmented female breasts, from breast augmentation and/or use of hormones. The sub-genres usually conform to certain conventions, and each may appeal to a particular audience. A pearl necklace is a slang term referring porn milf to a sexual act in which a man ejaculates semen on or near the neck, chest, or breast of another person. The related term twinkle-toes, which implies that a man is effeminate, hentai movies tends to be used in a derogatory manner. Squirt pornography involves women ejaculating. Am Abend , one of the earliest pornographic films that have been collected at the Kinsey Institute for Research in Sex, Gender, and Reproduction, starts with a female masturbation scene. It explores the more mental aspect of BDSM. Group sex is sexual behavior involving more than two participants. The higher pay scale and profile within a production often leads to group scenes where a straight actor only tops.