The Sound of Keys

When I was younger I could tell that my mom was nearby if I heard the sound of her keys jingling. No other key chain made that noise. I don't know exactly what the difference is in different key chains. I guess different keys make different noises and it's really unlikely for two people to have the same combination of keys and key chain(s). It's just amazing to me that you can tell the difference in the noise one set of keys makes over another.