**Core Concept**
The bluish green frothy discharge seen at the angle of mouth and nostrils suggests the presence of an antemortem or postmortem aspiration of a substance, leading to asphyxia. This scenario is characteristic of a specific type of poisoning.

**Why the Correct Answer is Right**
The bluish green color and frothy consistency of the discharge are indicative of chloroform poisoning. Chloroform is a volatile anesthetic that can cause respiratory depression, leading to asphyxia. When inhaled, chloroform can cause a bluish discoloration of the skin and mucous membranes, along with a frothy discharge from the nose and mouth. The liver enzyme cytochrome P450 is responsible for metabolizing chloroform, but it can also be broken down in the lungs, leading to the formation of phosgene, a highly toxic gas.

**Why Each Wrong Option is Incorrect**
* **Option A:** While carbon monoxide poisoning can cause a bluish discoloration of the skin, it typically does not produce a frothy discharge from the nose and mouth.
* **Option B:** Opium poisoning can cause respiratory depression, but it does not typically produce a bluish green frothy discharge.
* **Option C:** Cyanide poisoning can cause asphyxia, but it does not typically produce a bluish green frothy discharge.

**Clinical Pearl / High-Yield Fact**
Chloroform poisoning can cause a rapid onset of symptoms, including respiratory depression, unconsciousness, and death. It is a highly toxic substance that should be handled with caution.

**Correct Answer:** C. Chloroform poisoning.