Looking at even a single headless skeleton's body, which was much smaller than the bones of ancient creatures, the amount of special energy obtained after decomposition was nonetheless significantly greater.
Zachary casually channeled this energy into the isolated space within the Cave, speculating that this type of energy might be the "undead force" often mentioned in novels that allows undead creatures to keep moving ceaselessly.
Although undead creatures seem to never tire and possess endless stamina, they do experience some consumption during their activities. The energy they consume is what is known as the "undead force."
Speaking in more down-to-earth terms, the "undead force" can also be called death qi. This substance typically appears in graveyards or mass burial grounds. When living people come into contact with death qi, their bodies become weakened. With prolonged exposure, there will be tremendous changes in their spiritual demeanor.
