It is impossible to accidentally drink Hydrochloric Acid because it gives off copious amounts of fumes which burn the nose and eyes. A person would be coughing violently before ever taking a sip, so Mrs. Johnson could not accidentally drink it thinking it was water, even half asleep. Sulfuric acid on the other hand has almost no fumes and could easily be drunk by a person who is half asleep.
In the World War I era flashback, the date on the Washington Daily Tribune is given as Friday November 11, 1918. In reality, Armistice Day was a Monday.
Upon entering the hotel room in which Mr Mercado has committed suicide, Mr Mercado can be seen to blink once immediately after the camera cuts to his body in the chair.