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.
Passing kidney stones is agonizing, and giving birth is a prolonged kidney stone experience.
Huh. I'm guessing the pain of kidney stones comes in varying levels, because the one time I had them I wouldn't have called it the most painful thing in the world.
Then again, I could also have inherited my mom's pain tolerance, who gave birth multiple times without any kind of pain relief and without flinching.
I've read that passing a kidney stone through the urethra has a brief level of pain matching childbirth... but it's usually much briefer than childbirth.
Interesting. I suppose they're both objects with pointy bits much larger than the holes they're trying to pass through. On that note, I've been through very severe anal stenosis and THAT I would say was closing in on the most horrific pain I've ever been through. Before I could go to the doctor about it my wife basically had to spend all day and sometimes night keeping me occupied so I had something to do other than cry.