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.
It's true. They set out to be hyper-progressive science people, and in some ways succeeded. Their engineers were always decent, and when a factory could source the stuff they needed good stuff was built.