The precise definition of roles and self-identification is a common subject of debate, reflection, and discussion within the community. Following World War II, during a period of social repression when governments actively persecuted homosexuals, women developed networks to socialize with and educate each other. This is commonly called mature milfs double vaginal penetration or double stuffing. Mutual masturbation, mutual manual stimulation of the genitals between partners, can be a substitute for sexual penetration. Reading or viewing pornography, sexual fantasy or other erotic stimuli may lead to a desire for sexual release such as by masturbation. Commenting on why there are not as many female macrophiles, psychologist Helen Friedman theorized that because women in most societies already view men as dominant and powerful, there no need for them to fantasize about it. New York photographer Irving Klaw also published illustrated adventure/bondage serials by fetish artists Eric Stanton, Gene Bilbrew, Adolfo Ruiz and others. Most bisexual porn is made by small production companies rather than the major studios. The consensual submission of the submissive is sometimes demonstrated to others by symbols indicating his/her belonging to the dominant, such as wearing a collar, special tattoos, piercings, a very short haircut or a bald head. Common phrases used to refer to these individuals are chicks with dicks or the derogatory term shemale, although these are generally considered pejorative among transwomen. The resulting consent and understanding is occasionally summarized in a written contract, which is an agreement of what can and cannot take hentai videos place. Lesbian pornography typically videos porno gay features a wider range of appearances and body types than is typical of mainstream pornography. Point of view pornography is adult entertainment filmed to look as if the watcher were experiencing the sex act themselves. The term bondage describes the practice of Physical restraining. Such grounds and even the definition of pornography have differed in various historical, cultural, and national contexts.