Imagine you're walking down an English country lane one evening when you're struck by the feeling you're not alone. You turn, and a few yards away you see, in the fading light of day, the shape of what can only be described as a big black dog. It has shaggy hair and huge eyes, and it's watching you.
You walk on, trying to shrug it off, but every time you look back, it's there. Fear begins to creep in and you quicken your pace. You're nearly running when you reach your destination and, in a rush of courage, spin to confront your pursuer. But it's gone, vanished.
"Oh, yeah," one of the locals later tells you, completely unsurprised. "You've just seen a black dog."
