This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Unknown
Frequent blushing (“erethism”) is associated with : - 
Select and explain. 
A. Mercury, B. Lead, C. Phenolic acid, D. Carbolic acid
A: Mercury
Answer: A: Mercury 
Explanation: Mercury
Mechanism of toxicity.
Mercury reacts with sulfhydryl (SH) groups, resulting in enzyme inhibition and pathologic alteration of cellular membranes.
Clinical presentation. Acute inhalation
Severe chemical pneumonitis and noncardiogenic pulmonary edema.
Acute gingivostomatitis may also occur.
Chronic intoxication
Classic triad
Neuropsychiatric disturbances
Gingivostomatitis. Metallic taste
Frequent blushing (“erethism”).
Pain in the extremities,often accompanied by pinkish discoloration and desquamation (“pink disease”)
Reference – Poisoning & Drug Overdose by Kent R. Olson 3th- 213