Thun, it's not the pain part so much as the tingle that goes with the pain, funny thing is, our anatomy is set up so that after giving birth and nursing a child, the tug from the nursing on the breast helps to pull the vagina back into its pre-child shape, so when you tug, pinch or bite a woman's nipples, well the connection is almost immediate to the other female organs and so even though there may be pain, it is also stimulating sexually -- but with the understanding that every woman has her own reaction to this ... hope I didn't get too technical, but I find it fascinating....