Pedestrians' world is not a static one, but rather one which is constantly in flux. The pedestrian dynamics is subject to a wide range of influences and displays an interesting phenomenology. Along with collective self-organization phenomena (e.g., streams of people, rivers of people, collective synchronization), there are also a multitude of applications in the context of crowd management, design of pedestrian facilities and urban planning. Here, I address comments from the discussants of my review paper from the viewpoint of elementary physics laws paying particular attention to the self-organization phenomena in crowds.