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.
If you get into mindfulness meditation a little bit, the concept of self in general shifts in really weird ways. Like I know that I am an individual entity in the world, but the sense of an individual actor or driver within my consciousness has faded somewhat. When you recognize that the thoughts or feelings that manifest in consciousness are about as much under your control as whether the wind is blowing or what the people across the room are talking about, it gives you a new perspective on life.