To suffocate a sparrow quickly, it might need to be more than just a “toxic” level. Perhaps it was a mix of carbonaceous gases. If it had some carbon MONoxide in it, it would rapidly poison any red blooded creature.
What do you make of this claim in the article?
Indeed, the fumes coming from the depths of Hierapolis’ phreatic groundwater produced hallucinations.
(Other than the apparent redundancy.)