What is a sandworm? It's not a group of tiny insects in the sand, or insects as big as dogs found in the desert, but rather, it's a gigantic worm as thick and long as a train or subway, which can be understood as a super-sized roundworm.
The huge mouth of the sandworm houses dozens of rows of rotating saw-teeth, which like a mole burrower, allow it to move swiftly under the sandy gravel. Meanwhile, the sandworm grows by digesting the energy from the mineral crystals in the sand, and as for its excrement, that is the "hard stone" produced after the mineral crystals go through the high temperature, high pressure, and strong acid digestion inside the sandworm's body.
And this hard stone is the rare material known as "Ancient Granite"! This means that the stones Da Fei found nearby are all the excretions of the sandworm, which also implies that there are even more inside the nest, and possibly an unimaginable bounty of resources if the sandworm is killed!
