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.
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.