On a recent stay in Paris, France, I met these two girls at the street. One of those occasions were you might hesitate taking their picture, but they looked at me when I stopped and I asked to do a photo with them. They happily agreed if I just took one with their iPhone too. I often try to be fast and shoot before the people I capture are ready, because here the more interesting expressions often are present, and adds another dimension to the story. Therefore I started shooting before they were posing, and this captured another mood and feeling than afterwards.
When people look at the camera the expression and obviousness of being photographed changes the atmosphere and the photo becomes something different. Not that this means something less good, but different.