my friend's sister believed that menstrual blood was blue - because that is how it is portrayed on commercials for pads. when she had her first period, she screamed and freaked out because it was BLOOD!
A childhood belief about periods

others believed things like this
- 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 was horrified when my first period arrived. It wasn't blue, like in the commercials for sanitary towels.— Jane
- I thought pads sucked blood from women. It wasn't until later in life that I knew their actual purposeAnon
- I used to think that blood was blue until it touched air.— paetrw
- when I was young, I heard that blood had iron in it. I thought blood was red because it was rusty.— Hunter
- I used to believe period blood came from the nipples. I thought that was what "padded bras" were for!!Anon