Many transgender people regard the term shemale as offensive, arguing that it mocks or shows a lack of respect towards the gender identity and gender expression of transgender individuals; in this view, the term emphasizes the biological sex of a person and neglects their gender. A pornographic work is characterized as hardcore if it has any hardcore content, no matter how small. Sigmund Freud considered foot binding as a form nude milfs of fetishism. In humans, females generally have more round and voluptuous buttocks, caused by estrogen that encourages the body to store fat in the buttocks, hips, and thighs. Patricia Hill Collins, an African-American writer, theorizes that this is derived from a stereotype that those of black descent are promiscuous, and their buttocks are objectified by porn as a result. The phrase buttered bun is sometimes gay boy porn used to refer to the owner of the orifice in question. Most bisexual porn is made by small production companies rather than the major studios. Mammary intercourse is a sex act, performed as foreplay or as non-penetrative sex, that involves the stimulation of the male penis by the female breasts and vice versa. Irrespective of the legal or social view of pornography, it has been used in a number of contexts. Real medical hentai movies shots or videos may violate privacy laws in some countries. The reverse of this, in which nude women interact with clothed men, is called Clothed male, naked female . 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. It contains graphic sexual activity and visible penetration. A study of 164 males in Finland from two SM clubs found that 18.2% had engaged in coprophilia; 3% as a sadist, 6.1% as a masochist, and 9.1% as both. 18% of heterosexuals and 17% of homosexuals in the study pool had tried coprophilia, showing no statistically significant difference between heterosexuals and homosexuals. Bukkake pornography involves a performer, usually female, onto whom several men or women ejaculate, usually on the face.