Knocker

The Knockers are the mine-spirits of Cornwall — small, wizened, grey-bearded fairy folk, about two feet tall, who dwell deep in the tin and copper workings and make themselves known by the knocking sounds heard in the dark underground. Cornish miners regarded them with wary affection: the knocking was widely believed to be the Knockers tapping at the richest lodes, and many a miner followed the sound to a fresh seam of ore.

They had to be respected. It was reckoned unlucky to whistle or to swear below ground, to make the sign of the cross, or to fail to leave them a scrap of pasty-crust; treated well they were helpful, but mocked or cheated they would bring rockfalls and ill luck. Cornish miners carried the belief across the Atlantic to the mines of America, where the spirits lived on as the 'Tommyknockers'. The Knockers are a vivid expression of how a deadly trade peopled its darkness with spirits to be appeased.