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.
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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.