**Core Concept:** The stiffening of muscles after death is a natural phenomenon that occurs due to the loss of cellular potassium ions, which leads to the altered muscle contraction and relaxation. This process is essential for the proper preservation of the body during post-mortem examination.

**Why the Correct Answer is Right:**
Correct Answer: B. Postmortem rigidity (also known as rigor mortis) is the stiffening of muscles after death. This occurs due to the release of calcium ions from sarcoplasmic reticulum, which leads to actin-myosin cross-bridge formation and muscle contraction. As the heart stops pumping blood, oxygen and nutrients are no longer supplied to the muscles, causing cellular potassium ions to leak out, leading to muscle stiffness.

**Why Each Wrong Option is Incorrect:**
A. False stiffening of muscles due to rigor mortis is not a correct answer as rigor mortis is the correct term for the stiffening of muscles after death.
C. False stiffening of muscles following trauma is not relevant to the question as the question refers to the stiffening of muscles after death.
D. False stiffening of muscles due to inflammation or infection is not a correct answer as the stiffening described in this question is due to the loss of cellular potassium ions and the subsequent muscle stiffness.

**Why the Correct Answer is Right:**
Postmortem rigidity (B) is the right answer as it accurately describes the stiffening of muscles after death. The process is due to the release of calcium ions from sarcoplasmic reticulum, causing actin-myosin cross-bridge formation and muscle contraction. Additionally, the loss of cellular potassium ions leads to muscle stiffness.

**Clinical Pearl / High-Yield Fact:**
The process of rigor mortis provides valuable information to the medical examiner or pathologist during forensic investigations. It allows them to determine the post-mortem interval (the time elapsed since death), as the severity and duration of rigor mortis provide clues about the time of death and the body's position before death.