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.
Huh. Oddly I am allergic to shrimp and lobster, but love mushrooms. To me they don’t smell the same though. Though this fact probably explains why veg oyster sauce is mushrooms.