A woman who was dropped on her head when she was a baby and hence the sex center in her brain failed to shrivel and whither away, causing her to exhibit unnatural levels of sexual appetite. It is comparable to the rat with an electrode sticking in its pleasure center that is attached to a switch in his cage. The rat will keep flicking the switch till he is sexified beyond recovery. This is probably also what happened to Nickelodeon, although he seems to have got loose, unfortunately.
Even frustrated ones, like spuriousmonkey.