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.
I’m the opposite. I can’t ever ‘zone out’ while listening/watching/reading/playing stuff; I can’t even listen to music while playing games, and usually turn background music on low or off.