Nipple clamp
A nipple clamp is a type of sex toy that is applied to a person's nipples to pinch them. Varieties of nipple clamp include clothes-pin-style, tweezer and clover. Nipple clamps are used to cause pain in the nipples as part of certain BDSM activities. They are also used to produce erotic stimulation as part of nipple play. In this context they are not primarily used to produce pain but rather to increase nipple sensation. Their use traps blood in the nipples, increasing the sensitivity of the nipple. The sexologist Carol Queen says that "clamps are also very useful for hands-free nipple play".
Source: Wikipedia
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