Any movement causes the mercury filled ball to hit the deeper one, spreading vibrations through the vaginal area. Women primarily use them on their own, but they can also be incorporated into sexual activity with a partner. The testicles and the erect penis are slipped through the ring, which fits tightly, putting pressure on the dorsal vein of the penis. The idea is that the cock ring will keep the blood that has engorged the penis from flowing out. The man will therefore retain his erection longer and, theoretically, be able to prolong his sexual activity.
Some men also wear cock rings when they want their genitals to look larger under their pants.
Proper fit is important so that the penis and testicles do not get bruised. Caution is needed not to wear the rings too tightly or for an extended period of time, since they act as a tourniquet limiting blood flow and can cause severe damage to the genitals. These come in various scents and flavors and are primarily designed to make caressing and massage more sensuous, though some are used as lubricants for intercourse. The sensations and scents of creams, lotions and oils on the skin can be arousing for some people. The flavor of the cream or oil is often important for couples who want to have oral sex or like to kiss their partner's body all over.