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.
Metal has no taste tho. What yr tasting is you. VSauce or Nilered did a video about it.
You can test it yourself, just degrease and wash a coin. Once clean, no taste.
Of course it is not free metal. Probably oxide. And no, I am not going to taste rust.