In the local county museum, I'd found some information on very old local customs dating back to when witchcraft was allegedly widespread in the area. One superstition was to leave three iron nails on top of a door frame, apparently the devil can't abide iron, so the story went, making it impossible for him to hide on the door frame and jump on your back as you passed through the door.
Shortly after I was making changes to my daughters bedroom when we found a tiny old door which had been bricked up and plastered over. As we uncovered it we found - you guessed it -Three Iron Nails.
We left them there - can't be too careful.