origin: (1834) mɛθeɪnˈθaɪɒl; Medieval Latin; later German; mercurium = mercury + capere = to seize.
You know how sometimes you may pull up to refill gas in your car, or if there is a leak in your home, and you'd be prone to state, "I smell gas"...
Well, you don't, you smell mercaptan, which is pronounced like a mermaid sea-captain, but is actually the substance used in the process of replacing the oxygen of an alcohol with sulfur = thereby imparting it with a distinct odor, described as rotten eggs, garlic, cabbage, or smelly socks. Also known as thiol & methanethiol.
Gas actually has no smell to the human nose.
You'd easily suffocate to death and be none the wiser.
However, it's also an organic substance (organosulfur), which means that it can be found even in the human body. You'd have experienced this via flatulence, bad breath, and peeing after eating asparagus!
Less than one part per million is all it takes to make a person go, "Ew."
Unless you have a rare mutation in your genes, making you immune to the odor, as testified to here by a Mr. Niels Hoven: Specific anosmia, or why I can’t smell farts.