**Core Concept**
Contusion and postmortem staining are two distinct entities that can be easily confused due to their similar appearance. Contusion refers to the bruising caused by trauma that leads to bleeding into the soft tissues, whereas postmortem staining is the discoloration of the skin and underlying tissues after death due to the pooling of blood.

**Why the Correct Answer is Right**
The key difference lies in the timing and mechanism of occurrence. Contusion occurs immediately after trauma, whereas postmortem staining occurs after death. The bleeding in contusion is due to the disruption of blood vessels, whereas postmortem staining is due to the settling of blood in the dependent parts of the body after death. The blood in contusion is also more likely to be accompanied by other signs of trauma, such as swelling and ecchymosis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because contusion can occur without any external signs of trauma, making it difficult to distinguish from postmortem staining.

**Option B:** This option is incorrect because postmortem staining can occur in any part of the body, not just the dependent areas.

**Option C:** This option is incorrect because contusion can occur in any tissue, not just the skin.

**Clinical Pearl / High-Yield Fact**
When differentiating between contusion and postmortem staining, it is essential to consider the timing of the injury and the presence of other signs of trauma, such as swelling and ecchymosis. Remember, contusion occurs immediately after trauma, whereas postmortem staining occurs after death.

**Correct Answer: C. The presence of other signs of trauma such as swelling and ecchymosis in contusion.**