“The experience of pleasant pain is familiar to many, perhaps most, people. (Not you? Think again: ever enjoyed the pleasant muscle ache of a good day's exercise, or the challenging burn of a spicy curry?) Many more, although they may not be consciously aware of it, also have some experience with erotically arousing pain: biting, scratching, pinching, mild hair-pulling and hickeys have an honored place in many folks' sexual repertoire. If seeking out and/or eroticizing pain is sick, then it's a sickness about as rare as the common cold.”
Book:Spanking for Lovers