This sketch is from Project Prostitute, an online gallery of prostitutes drawn and submitted by people like your grandma and that woman at the deli whose missing a finger...all sorts of different folks. The creator calls it a "psychological experiment" and claims that drawing whores reveals "hidden parts" of people.
In the spirit of science, we've gone ahead and made some conclusions of our own based on this experiment. While people imagine prostitutes in all different shapes and sizes, they almost always have an exposed midriff...