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.
The fact that things are able to float, despite of gravity pulling all objects towards the big mass of Earth. You would think that the push of gravity should be more than enough to overcome the slight fluid displacement that allows balloons and boats to push away from the Earth’s surface.
Your comment has made me realise I don’t understand how floating works.
Think of the fact that pressure increases with depth, so when something is floating there’s a higher net pressure at the bottom than at the top which results in an upward force as the fluid tries to equalize.