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.
Soul mates are made, not found. You get with someone compatible to you, and through the sharing of experiences and affection, if nothing goes excessively wrong, they become unique for you.