The audience is not impressed, because they have heard the Die slide to the opposite compartment. They ask the magician to open the doors to the other compartment. The magician closes the doors to the first compartment. then tilts the box, the Audience can hear the die sliding over, then opens the doors to the adjacent compartment to show that it is empty. This business of sliding die from one compartment to the other is repeated, till the audience is howling for all four doors to be opened.
Finally, the Magician opens all four doors, and proves the die has in fact vanished. The solid die is found in hat, or some other container.