A 28-year-old woman from Delhi presents with acute onset dyspnea, chest pain, and syncope following ingestion of cyanide-laced food at a restaurant. On arrival, she is unconscious with severe metabolic acidosis (pH 7.1, HCO~3~^−^ 8 mmol/L), elevated lactate 12 mmol/L, and normal arterial oxygen saturation (SaO~2~ 98% on room air). Venous blood appears bright red. Which electron transport chain complex is irreversibly inhibited by cyanide, and why does oxygen saturation remain normal despite cellular hypoxia?