There is also some evidence that pornography can be used to treat voyeurism. Although pornography has usually focused on heterosexuality, due to the prevalence of the heterosexual orientation, explicit gay material has a long history as well, which reaches back to Greek antiquity, if not to prehistory. It is mutual consent that makes a clear legal and ethical distinction between BDSM and such crimes as sexual assault or domestic violence. Common phrases used to refer to these individuals are chicks with dicks, trannies, or shemales, although these are generally considered pejorative slurs among transwomen. Amateur porn has been called one of the hentai sex most profitable and long-lasting genres of pornography. Real enema shots or videos nude milfs of true medical situations may violate privacy laws in some countries. Bukkake videos are a relatively prevalent niche in contemporary pornographic films. 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. Central to the typical MILF narrative is an age-play dynamic of older women and younger lovers. The consent and compliance for a sadomasochistic situation can be granted only by people who can judge the potential results. Spanking or whipping pornography involves spanking or whipping, generally of the buttocks, with the hand or with other objects such as belts, switches, paddles, brushes, or whips. The name of the practice, when it is done in a repeated in-and-out videos gays motion, is derived from its passing resemblance to the dipping of a tea bag into a cup of hot water as a method of brewing tea. The fundamental principles for the exercise of BDSM require that it should be performed with the informed consent of all involved parties. Rape itself is a crime in many countries. As amateurs in a single segment of a multi-part video, the actresses are typically paid only about 50,000 yen .