I used to believe that the blood that came out during a woman's period was the blood that would go in a baby's veins if she were pregnant. I sort of understood the connection between not having periods if you're pregnant, but as for the rest, I didn't have it exactly right.
A childhood belief about periods

others believed things like this
- my aunt used to have an imaginary friend who instead of having blood had 7-up in her veins.Anon
- I thought the blue veins in some cheeses were actually blood vessesls!— Helen
- HA! I used to think when you got your period, you would just pee blood...I wish it was like that...if only.Anon
- I used to believe that when a woman was pregnant the baby could play monkey bars on her ribs.— Laura
- I used to believe that when a woman was pregnant, she fed the baby with a tiny spoon through her belly button.— Marie
- when I was young, I heard that blood had iron in it. I thought blood was red because it was rusty.— Hunter