If arsenic is a patient assassin, hiding out in the most recondite of the body’s tissues and accumulating there for years, cyanide takes your breath away. In sufficient concentrations, it stimulates the carotid body’s receptors all at once, triggering a reflex that cuts off respiration. Medical literature calls this the audible gasp that precedes tachycardia, apnoea, convulsions and cardiovascular collapse.
