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.
! I just assumed, lol
They have an episode where they talk about the birthday paradox and then follow it up with talking about how the math isn’t 100% correct as applied to humans bc birthdays aren’t normally distributed.
https://www.thisamericanlife.org/630/transcript#:~:text=A%20simple%20way%20to%20think,those%20two%20share%20a%20birthday.
ah, fair enough lol