In the scene in Okinawa, when Balck Mamba is talking to Hattori Hanzo, we see him cutting some food on the bar. When he is done with the knife, he tosses it, somewhat dramatically, to a magnetic knife rack mounted vertically on the wall behind him. The scene cuts away from that shot, but when it returns, the angle that the blade is resting on the magnet has changed. The cook did not move from his spot, and there is no reason to believe that the knife moved on its own.