**Core Concept**
Phosphorus poisoning is a well-known cause of dark brown postmortem staining and a characteristic garlic-like odor in the stomach. This is due to the formation of phosphorus-containing compounds, which are responsible for the distinctive color and smell. Phosphorus poisoning can occur through ingestion, inhalation, or skin absorption.

**Why the Correct Answer is Right**
Phosphorus poisoning leads to the formation of phosphorus-containing compounds, such as phosphorus acid and phosphine gas, which are responsible for the characteristic garlic-like odor. The dark brown postmortem staining is due to the deposition of these compounds in the tissues. Phosphorus poisoning can occur through various routes, including ingestion, inhalation, or skin absorption, and can lead to severe symptoms, including nausea, vomiting, and abdominal pain.

**Why Each Wrong Option is Incorrect**
**Option A:** Aniline dye poisoning is not typically associated with a garlic-like odor or dark brown postmortem staining. Aniline dye poisoning is more commonly associated with methemoglobinemia and a bluish discoloration of the skin and mucous membranes.

**Option B:** Carbon dioxide poisoning is not typically associated with a garlic-like odor or dark brown postmortem staining. Carbon dioxide poisoning can lead to respiratory acidosis and a range of symptoms, including headache, dizziness, and confusion.

**Option C:** Hydrocyanic acid poisoning is not typically associated with a garlic-like odor or dark brown postmortem staining. Hydrocyanic acid poisoning can lead to rapid onset of symptoms, including headache, dizziness, and respiratory failure.

**Option D:** (This is the correct answer, so we'll skip it for now.)

**Clinical Pearl / High-Yield Fact**
Phosphorus poisoning is often associated with a range of symptoms, including nausea, vomiting, and abdominal pain, and can be fatal if not treated promptly. It's essential to consider phosphorus poisoning in cases where a patient has ingested a substance with a characteristic garlic-like odor.

**Correct Answer:**
✓ Correct Answer: D. Phosphorus