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.
Cobalt is very toxic. Far worse than lead. But yet bound up in this one molecule, that looks like this:
it becomes biologically necessary for all animals. How does it get there? Is all the vitamin B12 made already and it stays in circulation, or is there some plant that selectively fetches cobalt from the ground and builds this thing that keeps us all alive?