This is all about the people you pass on the street. Think about it, when you are walking down a busy street (such as in New York) how many people do you actually notice? Do you even register that they have faces? When I see people walking down the street they seem to be lifeless robots who only want to get from A to B and I tried to portray both views. The view from the person walking and not noticing anything, and the view of the person who is just standing there, studying the faces of the people who pass them.
Note: It is a little dark, but I think that adds to the atmosphere.