**Core Concept**
Rigor mortis is the temporary stiffness of the muscles that occurs after death. It is a natural process that is caused by the changes in the muscle cells at the molecular level.

**Why the Correct Answer is Right**
Rigor mortis first starts in the small muscles of the body, such as those in the face, eyelids, and jaw. This is because these muscles are composed of more fast-twitch fibers, which are more susceptible to the changes in the muscle cells that lead to rigor mortis. The process of rigor mortis begins with the breakdown of ATP, which leads to the depolarization of the muscle cells. This causes the muscles to contract and become stiff. As rigor mortis progresses, it spreads to the larger muscles of the body.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided.
**Option B:** This option is not provided.
**Option C:** This option is not provided.
**Option D:** This option is not provided.

**Clinical Pearl / High-Yield Fact**
Rigor mortis typically begins within 2-4 hours after death and peaks at around 12 hours. It is an important forensic tool, as it can help estimate the time of death.

**Correct Answer:** .