## **Core Concept**
The question pertains to the phenomenon of **cadaveric rigidity**, also known as rigor mortis, which is a well-known post-mortem change. Rigor mortis is a transient stiffening of muscles after death, caused by changes in muscle proteins. The duration of rigor mortis can be influenced by various factors, including environmental conditions and the presence of certain substances.

## **Why the Correct Answer is Right**
The correct answer, **D. Datura**, relates to the fact that **Datura** (or other anticholinergic substances) can cause **delayed** or **prolonged** rigor mortis. This effect is not commonly seen with other types of poisoning listed. Anticholinergic substances can interfere with normal physiological processes, potentially affecting the duration of post-mortem changes.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Typically causes **earlier onset** and **shorter duration** of rigor mortis due to its effect on ATP depletion.
- **Option B:** Not commonly associated with significant alterations in the duration of rigor mortis in a way that's notable or specific enough to be a clue for poisoning.
- **Option C:** Usually does not have a significant impact on prolonging rigor mortis.

## **Clinical Pearl / High-Yield Fact**
In cases of suspected poisoning, the duration and characteristics of rigor mortis can provide valuable clues. A prolonged rigor mortis might suggest poisoning with substances like **Datura**. However, it's crucial to consider this in the context of other clinical and forensic findings.

## **Correct Answer:** . Datura