Kickback, sometimes referred to as knockback or rarely as an obeisance, is a penalty for using a Resonance Soul.
Many Resonance Souls have kickbacks are not normally seen or felt, while others can have enormous prices to pay. In rare cases, a Rez may have a kickback that is unknown, or there is assumed to be no kickback.
Some kickbacks are physical, others are mental or occur within the personality. An example of a physical kickback is a headache resulting from turning a piece of the body to stone while a mental kickback may be the loss of memories from regenerating flesh, or the increase in paranoia from the manipulation of soundwaves.