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.
May I ask what is special about cobalt in B12 specifically? I've come to realize there are numerous inorganic substances inside my body like copper, gold etc. so cobalt by itself doesn't really stand out anymore.
Cobalt by itself is toxic and damages the nervous system.
Interesting