During the examination of a body dead for approximately 18 hours, the forensic expert notes that the rigidity of the limbs can be easily overcome by…

Secondary flaccidity occurs after rigor mortis passes off (usually after 36 to 72 hours, depending on conditions). Once secondary flaccidity sets in, the muscles are soft and limp because putrefaction has broken down the muscle proteins (actin and myosin). If rigor mortis is forcibly broken while it is still present (within the first 24 hours), it does not return, but the muscle fibers undergo mechanical tearing. At 18 hours, rigor is usually fully established or beginning to pass; however, if the question describes muscles that can be easily manipulated without returning to stiffness because rigor has resolved, it is secondary flaccidity. Wait, if rigor is broken before resolution, it does not re-form. But the prompt states 'rigidity of the limbs can be easily overcome... permanent structural tearing'—actually, breaking rigor mortis before full development causes tearing and it does not re-form. Let's look closely at standard text: Nysten's law and rigor timeline. At 18 hours, rigor is fully developed. If it is broken by force, it never returns. Secondary flaccidity occurs after 2-3 days when putrefaction destroys the cross-bridges. The specific phrasing 'rigidity can be overcome by force and does not return' describes the forcible breaking of rigor mortis.