The fragments are sustained by what they are: fractions of souls. Without consuming others, they inevitably wither into nothing.
In their dormant stone form, they expend almost no energy. For this reason, they seldom emerge unless stirred by the nearness of a ripe passage or disturbed by outside force, such as a fracture. Even when cloaked, they conserve themselves, avoiding risks on unripe prey if a better vessel is within reach.
Inducing, however, is costly. Each memory they alter in the prey must be paid for with one of their own. The longer the process, the more their essence drains away.
For the prey, each alteration has the opposite effect. Every memory twisted erodes the bond tying the soul to its body, loosening its hold and drawing it closer to departure.
Thus, in every encounter, both predator and prey are diminished: one spending its memories to sever the bond, the other losing its grip on existence with each thread unraveled.