A childhood belief about mirrors

When I was 7 and 8 years old, I used to believe that my reflection (image) in a mirror might be another "me" in a world identical to this one (but opposite), thinking identical thoughts, and I was his reflection as he was mine. In his eyes, I could understand and 'see' what he was thinking, because I was thinking it myself.

I thought my echo was his voice.

I don't know why, but I was terrified of reverberation-type echoes in restrooms until I was 8 or 9, and I used to think your 'shadow' was a part of you which could be lost, like in Peter Pan (e.g. you only had one).

But mostly, I remember the mirrors. I'd stare into my eyes thinking his thoughts. My mother thought I was vain because I spent so much time at the mirror.