I've just been thinking about this as I've been lay in the bath.
I'm currently pregnant and baby goes mad when I'm in the bath and I was watching him kicking and squirming inside me and just thought... This is actually pretty odd when you think about it. I have a living thing that's moving around inside me!
A friend had to have a blood transfusion not so long ago and she can't think about that for long without feeling squeamish that someone else's blood was inside her!
What other things do you find strange when you really think about them?