The black coffin was exposed to air. There was no tombstone nor a coffin lid. Angor could clearly observe the skeleton inside.
It looked like someone small. From a quick assumption, the skeleton belonged to someone about 1.2 or 1.3 meters tall. A child, probably.
Next, he glanced at something shining around the skeleton's skull. He saw the object during the last lightning flash.
He reached for it and found a necklace, which was made from a platinum chain and a heart-shaped gem. The gem was polished into a hexadecahedron[1.16-faced entity], which shone brilliantly each time more lightning came.
Angor moved a finger around the gem and found a small trigger.
Click!
Another secret chamber was revealed in the gem.
As he expected, the gem was polished in this way to confuse human sights. The design concealed the fact that the gem was only a thin shell, while more space existed inside.