Some POV/gonzo porn sometimes breaks the strict point-of-view convention. The activity is done by itself or as a part of or prelude to other activities which many times involve sex. The cover is open while the submissive lies down on his back and places his head in the box. Works in this genre may explore philosophical, political or social issues. Often other friends and community members may witness the signing of such a document in a ceremony, and so parties violating their agreement can result in loss of face, respect or status with their friends in the community. When used as an alternative to penile-vaginal penetration, the goal may be to preserve virginity or to prevent pregnancy. Lolita pornography that features actual teenage girls under the age of 18 is illegal in most countries and treated as child or youth pornography. Additionally, the buttocks give an indication of the shape and size of the pelvis, which impacts reproductive capability. Pegging films include Strap It On , Babes Balling Boys , Strap Attack, Strap-on hentai videos Sirenz, Strap-on Chicks, Boss Bitches , various movies produced by LEDA Studios, momsex and San Francisco-based Men In Pain. Female masturbation involves the stroking or rubbing of a woman vulva, especially her clitoris, with an index or middle fingers, or both. Coprophilia , also called scatophilia or scat , is the paraphilia involving sexual arousal and pleasure from feces. Top and dominant are widely recognized for those partner in the relationship or activity who are, respectively, the physically active or controlling participants. The genre presents itself as real couples having gay cock real sex. This is commonly called double vaginal penetration or double stuffing. The glans itself may widen and lengthen as the stimulation continues, becoming slightly darker in colour, while the gliding action of the foreskin reduces friction. Perhaps following the example set by gay pornography, they have become a popular subgenre within heterosexual pornography since the turn of the century, featuring both vaginal and anal ejaculations.