I used to believe that we only breathed when we were asleep, since I only "heard" myself breathing when I was lying down.
A childhood belief about sleeping

others believed things like this
- I used to believe that if I fell asleep lying on my front that my boobs wouldn't grow. And they didn't.— Booey
- I used to believe that if you crossed your fingers when you were lying, you weren't really lying.— jo
- I used to think farts were air you had breathed in and out loads of times and was 'used'Anon
- i used to believe that if you swallowed gum, when you breathed in, your stomach would stick to your back— cope
- I used to believe that if I pumped in my sleep and breathed it in I would turn into a rotting turnip!— Quako
- I thought everyone only had a set number of breaths before they died.
I breathed slowly for a long time.Anon