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.
Sorry, I wasn’t clear. I understand how tides work; the source of my confusion is the person I replied to both stating that they don’t exist and explaining how they work, which is mutually contradictory: if they don’t exist, how can they work at all?