When I was about 5 or 6 I used to believe that "smoking grass" meant putting a long piece of grass in your mouth the way farmers do.
A childhood belief about smoking

others believed things like this
- Long grass with black seeds were really ant hotels, and the seeds were sleeping ants.— angelsheep
- I used to think that dandilions were marshmallows on grass— Vernon D'Souza
- I use to think mountains were dead dinosaurs and grass grew over it.— Tara
- When I was a kid I thought praying mantises were made out of grass— Landon
- I thought hills were dragons sleeping under the grassAnon
- That eating grass was a sure fire way to gain superhuman powers.— Brendan