Janitor Opens A Mysterious Box Left Outside The School On A Wintry Evening And Is Left Speechless

Moving?

The janitor went inside the cafeteria and found the box lying on the floor. A frown appeared on his forehead. He knew he left the box on the table. It is not empty for sure to be moved around by the wind, even though the box is obviously indoors and there is no wind here. How did it fall on the ground?