Others consider the position to involve the man squatting over his reclined partner while the testicles are repeatedly raised and lowered into the mouth. The warm sensation felt when urine trickles on the body seems to give very relaxing and pleasurable feelings to the person. Bra pornography involves women or men dressed in bras. 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. Penetration may involve use of fingers, toes, sex toys, or penises. Softcore pornography that does not contain ejaculation sequences is produced both to respond to a demand by some consumers for less-explicit pornographic material, and to comply with government regulations or cable company rules that may disallow depictions of ejaculation. Contrary to the other two types, B/D does not define the Tops and Bottoms itself, and is used to describe the general activities with either partner being the receiver and the giver. Cheerleader mature milfs pornography involves pictures of cheerleaders, both staged and real. No causal relationship is known between masturbation and any form of mental or physical disorder. Coprophilia , also called scatophilia or scat , is the paraphilia involving sexual arousal and pleasure from feces. Upskirt and Downblouse pornography features staged filming up women skirts or down their blouses while in public. Some prefer a particular type of clothing to urinate. Tentacle erotica features tentacled creatures raping or otherwise penetrating women or men. Individual tastes and preferences in the area of sexuality may overlap among these areas, which are discussed separately here. Behind the Green Door was one of the first pornographic films to feature sex between a white actress with a black actor . Gonzo hentai videos pornography gay cock is a style of pornographic film that attempts to place the viewer directly into the scene. Milking pornography features lactating women being milked or milking themselves .