In a Cup of Tea - A Ghostly Reflection in a Mirror

The idea of looking in a still pond and seeing your reflection goes back as far as the history of the Earth. I think there's very clearly a natural anxiety people have about things they might see in a mirror that they don't expect to. And like a lot of old ghost stories concern this, but horror movies today are still reproducing this effect. There's something behind your shoulder that you didn't expect to see there.