Human penises are generally cylindrical shaped with a bulbous structure at the end of them called a "glans"; they are sometimes referred to as having a "mushroom" shape. Humanoid penises may feature a foreskin that slides over the glans when the penis is flaccid, or they may have the foreskin removed ("circumcised"). Canine penises are usually contained within a sheath. The base of the glans swells like a large bulbous knot when erect. The feline penis is a type of tapered penis which has (depending on species) anywhere from a few to hundred sharp, backwards-facing barbs that stick out from the shaft during sex. Notably short and pointy compared to most species, it also features an extended sheath (not to be confused with medial ring). Equine penises are characterized by a distinctive blunted head, mottling of colors, a flared or "mushroomed" head, a medial ring, and/or a ring of flesh near the sheath. A cetacean penis is a tapering penis that looks something like a thick tongue or tentacle. Typically seen emerging from a genital slit.