To begin, there are some people who derive an extreme pleasure out of being whipped or burned or beaten. There is no rational explanation for this strange, delight. The fact remains that they react pleasurably to pain. These people are called masochists. Similarly, there are other people who derive the same pleasure out of being the ones who inflict pain or perform the beating. Their abnormality, too, is inexplicable. They are called sadists.
The point is this: these people have these strange desires in extremes. But normal people have similar desires but they are not so strong. They are present only in minute degrees. That is why some of us deliberately uncover ourselves in cold weather or continue to pick at a sore tooth although the act pains us. It is for this reason that most of us are able to derive pleasure from the “pain kiss.”
The “pain kiss” is simply a tiny bite, a love nip.
Catullus, who knew his kissing, if we are to judge from the many poems he left on the subject, once rote:
Whom wilt thou for thy lover choose?
Whose shall they call thee, false one, whose?
Who shall thy darted kisses sip,
While thy keen love-bites scar his lip?