If you stand in Tiananmen Square and keep your eyes open on a normal day, you will see the tour groups with their "keep together" flags, and the long line waiting to see the mummified Mao in his mausoleum, and the crowd around the entrance to the Forbidden City. Souvenir salesmen ply their trade where once the students massed around the Goddess of Democracy. And then you notice the militia vans endlessly circling, and the buses parked off to one side. It's a big space to police, and its vast openness makes it impossible to close off. Every few days, a group of supporters of the Falun Gong movement will suddenly unfurl their banners and wave them until the forces of order arrive, sweep them up and carry them away.