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.
That the first civilian hot air balloon was perceived as a flying monster by rural French onlookers who tried to bring it down before beating it with sticks.
Makes the whole Hartlepool monkey story seem sane.
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