For me it is the fact that our blood contains iron. I earlier used to believe the word stood for some ‘organic element’ since I couldn’t accept we had metal flowing through our supposed carbon-based bodies, till I realized that is where the taste and smell of blood comes from.
A solid that isn’t undergoing any sort of chemical reaction isn’t going to smell because there isn’t anything to smell. You need a molecule to enter your nose to smell. That’s my basic understanding, someone smarter than I can explain it better.
Also I’m not sure any country still uses iron for coins.
Iron would be a terrible metal for coinage, since it would shed rust all over everything after being handled. Some coins might be cast from iron (if it’s cheaper than alternatives, idk) but plated in other metals to prevent that.
Only faerie-adjacent realms still use iron coinage, because it keeps the little fae bastards from picking your pocket.