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 term discipline describes psychological restraining, with the use of rules and punishment to control overt behavior. Twink pornography features younger performers, and usually features young men under 30 who identify as gay or bisexual. Sadomasochism does not imply enjoyment through causing or receiving pain in other situations . Fantasies of group sex are extremely common among both men and women, and group sex is a subgenre in pornographic films. The terms can be complimentary or pejorative. While bondage is a very popular variation within the larger field of BDSM, it is nevertheless sometimes differentiated from the rest of this field. The nipples are erogenous zones, and vigorous stimulation of them during masturbation usually causes the penis to become erect more quickly than it would otherwise. The buttocks in human females thus contain more adipose tissue than in males, especially after puberty. Lesbianism has been a theme in erotic art since at least the time of ancient Rome, and many regard depictions of lesbianism to be erotic. Crying pornography that features participating actors crying. Can also include auto-fellatio, or performing oral sex on oneself. Body parts including fingers, tongue and penis may be used for anonymous oral, vaginal and/or anal intercourse. One or more of the participants may engage in autoerotic sexual activity, such as masturbation, possibly without physical contact with the other participants. A female dominant in a master/slave relationship is often termed a Mistress, not to be confused with the colloquial usage of mistress as a kept sexual partner without a similarly formalized power relationship. Softcore pornography generally black gay porn contains nudity or partial nudity in sexually suggestive situations, but without explicit sexual activity, sexual penetration or extreme fetishism, while hardcore pornography may contain graphic sexual activity and visible penetration, including unsimulated sex scenes.