**Core Concept**
Carbon monoxide (CO) poisoning is a toxic effect caused by the inhalation of CO, leading to tissue hypoxia due to the formation of carboxyhemoglobin (COHb). This condition impairs the delivery of oxygen to vital organs, ultimately resulting in cellular asphyxiation.

**Why the Correct Answer is Right**
The cherry-red discoloration observed in CO poisoning is due to the presence of COHb in the blood and tissues. When CO binds to hemoglobin, it forms a stable complex that cannot release oxygen. This leads to tissue hypoxia, causing cellular injury and death. The cherry-red coloration is a characteristic postmortem finding in cases of CO poisoning, making it a useful diagnostic clue.

**Why Each Wrong Option is Incorrect**
* **Option A:** Cyanide poisoning also causes tissue hypoxia, but it does not produce a cherry-red discoloration. Instead, it leads to a blue or purple discoloration due to the formation of methemoglobin.
* **Option B:** Hydrogen sulfide poisoning causes a greenish discoloration due to the formation of sulfhemoglobin.
* **Option C:** Methanol poisoning causes a characteristic anion gap metabolic acidosis, but it does not produce a cherry-red discoloration.

**Clinical Pearl / High-Yield Fact**
In cases of suspected CO poisoning, it is essential to obtain a carboxyhemoglobin (COHb) level from a blood sample, as this can help confirm the diagnosis and guide treatment.

**Correct Answer: C. Carbon monoxide**