**Core Concept**
Rigor mortis is a well-documented phenomenon in forensic medicine, characterized by a stiffening of the body's muscles following death. This process is influenced by various factors, including the body's temperature, the type of muscles involved, and the time elapsed since death.

**Why the Correct Answer is Right**
Rigor mortis typically begins to set in 2-4 hours after death, as the energy stores in the muscles are depleted and the actin and myosin filaments become locked in a rigid state. This process reaches its peak between 12-24 hours post-mortem and gradually resolves as the body returns to a more relaxed state. The onset and duration of rigor mortis can be affected by environmental factors such as temperature; in warmer conditions, rigor mortis may develop more quickly, while in cooler conditions, it may persist for longer.

**Why Each Wrong Option is Incorrect**
**Option B:** Rigor mortis is not strictly limited to a specific time frame based on the season, although temperature can influence its onset and duration. However, the duration of rigor mortis in summer is typically longer, ranging from 36-72 hours, rather than 18-36 hours.
**Option C:** Rigor mortis does not necessarily disappear in the same sequence as it appears. While the initial areas of rigor mortis may resolve first, subsequent areas may persist for longer, leading to a complex and variable pattern of resolution.
**Option D:** The duration of rigor mortis in winter is generally shorter, ranging from 12-36 hours, rather than 24-48 hours, due to the lower body temperature which accelerates the resolution of rigor mortis.

**Clinical Pearl / High-Yield Fact**
It is essential to note that rigor mortis can be influenced by various factors, including the presence of certain medical conditions, such as muscular dystrophy, or the use of certain medications that can affect muscle tone. Forensic investigators should be aware of these potential confounding factors when interpreting rigor mortis in a post-mortem examination.

**✓ Correct Answer: A. Seen immediately after death**