Well i got told by my dads side of the family that if you stuck you thumb in your mouth and held your breath you would get bigger boobs. They told me my aunty did it when she was little so i had to try it. Sadly when i was 12 i developed the theory behind it as well and told my niece. See when you hold your breath the air tries to get out and the pressure has to be released so it goes straight forward....making your boobs bigger. Of course this isn't only for girls, because guys don't have boobs, when they hold their breath/blow on their thumb it goes into their muscles.
A childhood belief about rude bits

others believed things like this
- If you hold your breath and make a wish under a highway tunnel it will come true....I still hold my breath :)— aj
- I used to believe that if you rubbed butter on your boobs they would get bigger......— Daphne Johnson-Will
- when i was a little kid. i used to think that when u hold ur breath ur heart stops.. LOL :P — Annonymus
- I still hold my breath when I pass by cemetaries because it is impolite to breathe when other people can't.— Crystal
- My niece believed that the longer I breastfed my baby the smaller my boobs would get. She was 4 at the time.— M
- WHEN I WAS LITTLE I USED TO THINK THAT GIRLS GET BOOBS BY ONE DAY GOING TO SLEEP AND IT JUST HAPPENS— J.C