## **Core Concept**
Post-mortem lividity and contusion are two distinct changes that occur in the skin after death or injury. Understanding their differences is crucial in forensic pathology. **Post-mortem lividity**, also known as livor mortis, refers to the discoloration of the skin due to the pooling of blood in the dependent parts of the body after death. On the other hand, a **contusion** is a type of injury that results in bleeding into the soft tissues, usually caused by blunt trauma.

## **Why the Correct Answer is Right**
The correct answer highlights that post-mortem lividity **does not blanch on pressure**. This characteristic differentiates it from a contusion. When the skin is pressed, the blood in a contusion can be temporarily displaced, causing the area to blanch (turn pale). However, in post-mortem lividity, the blood has settled and does not move with pressure; hence, the area does not blanch.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because post-mortem lividity indeed occurs after death, which is a correct statement but does not directly address the differentiating feature from contusion.
- **Option B:** This option is incorrect because both contusions and post-mortem lividity can present with discoloration of the skin; hence, this is not a distinguishing feature.
- **Option C:** This option might seem plausible but is not the best distinguishing feature.
- **Option D:** This option is incorrect because it inaccurately describes a characteristic of post-mortem lividity.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **post-mortem lividity typically appears within 30 minutes to 2 hours after death and becomes fixed within 8-12 hours**. It also **does not blanch on pressure**, which is a critical distinguishing feature from contusions. This characteristic can be crucial in forensic analysis to differentiate between ante-mortem and post-mortem changes.

## **Correct Answer:** D. does not blanch on pressure.