These two photos illustrate the key difference between voyeuristic disorder and frotteuristic disorder: physical contact. This man on the left may just be birdwatching, but some people with voyeuristic disorder may use binoculars to spy on people who are naked or engaged in sex. In contrast, frotteuristic disorder involves physical contact, and a crowded subway car is the kind of place where someone with frotteuristic disorder may find opportunity for physical contact.