**Core Concept**
Postmortem lividity, also known as hypostasis or livor mortis, is the discoloration of the skin that occurs after death due to the pooling of blood in the dependent areas of the body. This phenomenon is a result of the cessation of blood circulation, leading to the settling of red blood cells in the microcirculation.

**Why the Correct Answer is Right**
Postmortem lividity is unlikely to develop in cases where the body has been subjected to significant external pressure, preventing blood from pooling in the dependent areas. This is because the pressure prevents the red blood cells from settling, thereby inhibiting the formation of lividity. In such scenarios, the blood is forced to remain in the upper extremities, thereby preventing the characteristic discoloration of the skin.

**Why Each Wrong Option is Incorrect**
**Option A:** This option may not be relevant to the topic of postmortem lividity. External pressure does not directly impact the formation of lividity.
**Option B:** This option may be a distractor as it does not directly relate to the formation of postmortem lividity.
**Option C:** This option is a distractor as it refers to a different phenomenon altogether. Postmortem lividity is not related to the formation of rigor mortis.

**Clinical Pearl / High-Yield Fact**
It is essential to note that postmortem lividity is a crucial indicator of the position of the body at the time of death. The pattern and distribution of lividity can provide valuable information regarding the circumstances surrounding the death.

**Correct Answer: C.**