The actual acts of urinating and defecating have thus become secondary social gestures. Bison and many of the cattle group have a prepuce tassel, a tuft of hair hanging from the foreskin around the penis opening. The tuft is a scent disseminator, but may have a visual role as well, for it is contrastingly colored. Carnivores, meat-eating animals, almost universally have anal glands with which they anoint the feces, giving it a musky odor in addition to the odors of bacterial incubation. The other type of signal comes from the sexual overtones of different ways of urinating.
Many mammals dramatize their sexual differences in urination posture.
Because of the usual differences in social stature between the sexes, genitalia have also become important signals of maleness and femaleness, aggression and submission, and the genitals have evolved specialized social ornamentation only obliquely related to the ancestral copulatory role. Few things harbor as many human taboos as the anal and genital organs. Movements or intentions of movements have become incorporated into many gestures of social behavior. Decorated appendages with contrasting lines and splotches dramatize these gestures. The two dominant themes are coming toward or escaping and going away from.