The slab reduces and not fitting into it's place any more it falls with extra loud noise - falling into the open pit.

Followed by minor rubble, dust and sand fall you can soon seen through into the tunnel: A moss-covered corridor extends beyond the fallen door. Tree roots hang from the sagging ceiling, and the air reeks of rot and damp. Ahead, a bas-relief carving of a bearded devil's face adorns the wall at a T-shaped intersection. The devil's open mouth is a well of utter darkness.
A hunched figure appear a moment later from the west of a T-shaped intersaction. Dwarf sized creature, wearing a mask that is a replica of the devil face at the tomb entrance. It glares at you just a moment. Without saying a word, the figure steps east and out of sight.