Accompanied by the gradual retreat of the accumulated water, those black snakes seemed to possess the same burrowing ability as earthworms, and as the water receded, they all burrowed into the deep mud. It was because of this that even though Zachary had discovered their location at that time, he still let them be.
After all, if there were only a few black snakes lurking deep underground in the camp, the survivors might spend a considerable amount to capture or kill them in order to eliminate potential hazards.
But once the survivors knew that there were countless black snakes deep beneath the campsite, they would probably choose not to spend more to exterminate those underground black snakes, but rather to move away from there. If temporarily unable to move, they basically chose to ignore this matter.
Only when the hidden dangers deep underground reemerged did people face the dangers they were about to encounter.