Pain does not have to be sharp; the most profound agony comes from "deep-seated resonance."
Forensic Report C-03 records: The material of the [Withered Bone · Spine Ruler] has undergone years of dehydration and mineralization, pushing its density $\rho$ close to that of biological bone. According to the impulse-momentum theorem $F \cdot \Delta t = \Delta p$, due to the extreme rigidity of the leather ruler, the contact buffer time $\Delta t$ with the human body approaches zero, causing the impact force $F$ to explode within milliseconds.
This is not striking the flesh; this is "impedance matching."
When this ruler hits your spine, the vibration frequency generated resonates with the natural frequency of the bone. The energy does not dissipate on the skin's surface but is channeled directly into the marrow. This blunt agony travels along the central nervous system, triggering systemic paralysis and trembling. We term this physical phenomenon "Divine Prostration"—in the face of absolute density, your bones will surrender long before your will does.