For quite a long time, I used to believe that during the period there's a blue liquid instead of blood! It was because of all those Always commercials at TV...
A childhood belief about periods

others believed things like this
- I was horrified when my first period arrived. It wasn't blue, like in the commercials for sanitary towels.— Jane
- I used to believe that menstruation fluid was blue because of the way TV commercials showed it. — matias
- 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 if you left crumbs out for a long period of time, they would turn into ants.— Bylaberrie
- I used to think that blood was blue until it touched air.— paetrw
- I used to believe period blood came from the nipples. I thought that was what "padded bras" were for!!Anon