Gonna add that this would tie in to the Shin's reverence for stone: perhaps it's needed in forging a new Parshendi body, perhaps by mixing it with the corpse. And, of course, messing with a corpse stops the rebirth; Parshendi go crazy when they see people desecrate corpses because those people basically killed those in the "time-out" zone, which, in addition to being, well, murderous, is also dishonorable.