When i was young i don't know why but i always thought that if you flushed the toilet during the night, a monster would come out and pull you in.
To this day i grimace at the thought flushing the toilet when its dark even though i don't remember how i came to the conclusion in the first place.
A childhood belief about fear of

others believed things like this
- I used to believe that monsters lived in my toilet and they ate my poop and urine when i flushed the toilet.Anon
- I used to believe that if I flushed the toilet before I showered, I would take a shower in dirty toilet water.— Chris D
- I used to think if I left the toilet seat open my cat would get flushed down the toilet.— G
- I used to think if you didnt get up before flushing the toilet would eat you...Anon
- i used to think when it started raining it was god flushing the toilet— edel
- I was certain that rain was created by God having a pee and flushing his huge toilet above us— Emma H