The female sex organ most sensitive to touch is the clitoris. Therefore, female masturbation almost always involves stimulating the clitoris, either by hand or with a vibrator. Many women also enjoy the feeling of fingers or a sex toy in the vagina, but this is a secondary sensation that is not necessary for orgasm, and that rarely results in orgasm on its own. Some women find stimulation of the front vaginal wall particularly pleasurable. The anus is rich in nerve endings and is also sometimes stimulated during masturbation, as are the nipples.