One of my friends who used to live in Japan told me a story ( I was 14 then, I think ) about monsters called "Kyoma Demons" that live in mirrors and look just like you, but if you turn your back they show their true form and emerge from the mirror to grab you and pull you into an alternate universe, and you would be trapped in the mirror while they lived your life. I still find it hard to go to the bathroom without a wrench, hammer, or some other blunt object to defend myself.
A childhood belief about mirrors

others believed things like this
- when i was young i used to believe that my image on a mirror would come to life if i broke the mirror.Anon
- I thought that every TV show was filed live, and I always wondered why they never messed up.— Steve
- one of my friend's was told by his father that if you didn't turn mirrors over the reflection would run out.— pri
- i used to think, when i was about 4 that i lived inside a whale because i live ion the country Wales— mike
- I used to believe you could live down the back of the sofa...— Big Pete
- I thought Oklahoma was a place in Japan (due to it weird name :P), and Japan gave it to USA later.— Luiz Alfonso