We're fascinated by images of people having sex because, beyond the titillation aspect, getting to watch others engage in intimate activity breaks so many taboos. Sex, we're taught, is a private matter between two loving people. How incredibly naughty then to be able to observe others in the act, either by watching a video or through the camera of our mind as we read an explicit book. Best of all, it's a sneaky vice — no one knows we're getting our kicks this way!

The fascination doesn't end with what takes place in the viewable arena — our fancies are tickled by the thought of celebrities having appeared in skin flicks during the early phase of their careers or of otherwise irreproachable members of the community being found to have vast libraries of pornography stashed away. As always, the discovery of the seamy truth about another plays a major part in the enjoyment aspect of these legends.