When my nephew was very young he persistently picked his nose. I told him that if he didn't stop, his head would cave in. He started crying hysterically, even his mum couldn't stop him. I felt a bit of a prat trying to explain what had happened, considering I was 26 at the time and should have known better!
A childhood belief about picking my nose

you weren't the only one
44 of you believed this
- when i was little my mum used to tell me if i picked my nose too much my brain would fall out!!! think it did— Maz
- I used to believe that if you picked your nose then your head would cave in!— Sir Jared
- I heard a mother in the street tell her young son not to pick his nose...because his head would cave in. — Ruby
- my mum once told me if you picked your nose your brains came out!!!!— smiley : )
- My wife used to tell our kids that if you pick your nose your brains would fall out— grampy
- i used to belive that if i picked my nose my head would cave in— me