A Boggart is an evil household fairy from English folklore which causes things to disappear, milk to sour, and dogs to go lame. Always malevolent, the boggart will follow its family wherever they flee. In Northern England, at least, there was the belief that the boggart should never be named, for when the boggart was given a name, it would not be reasoned with nor persuaded, but would become uncontrollable and destructive.
It is said that the boggart crawls into people's beds at night and puts a clammy hand on their faces. Sometimes he strips the bedsheets off them. Sometimes a boggart will also pull on a person's ears. Hanging a horseshoe on the door of a house is said to keep a boggart away.
In the folklore of North-West England, boggarts live under bridges on dangerous sharp bends on roads, and it is considered bad luck for drivers not to offer their polite greetings as they cross.