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.
Time relativity always boggles my brain, I accept the fact but I find crazy that if I strap my twin and his atomic clock to a rocket and send them out to the stratosphere at the speed of light, when they return he'll be younger than me and his clock will be running behind mine. Crazy
Please dont do that