jdmklein | rhetorical question

Master woke up this morning in a mood to inflict some pain. i, of course, was delighted at the prospect. The pulled hamstring in my leg, on the other hand was not at all in the mood. As Master worked on the left side of my body i traveled between paroxysms of sensual, sexual joy and overwhelming helplessness. When He began working on the right side of my body, the hamstring tensed up and dropped me immediately into a world of totally unerotic pain.

How can one type of pain be so darned erotic and another just be plain full of hurt?