No, before you read on and possibly disappoint yourself, this Entry isn't about Dolly Parton or any other examples of large mammary glands commonly found on post-pubescent female humans1. Nor is it about those things that adorn the doors of some houses, begging to be smacked against the hard wood in order for the occupant to become aware of someone attempting to gain access.
It is in fact referring to a part of Cornish folklore. The tin miners of the region believed that there were helpful spirits in the mines, who could be heard hammering at places where there was a good lode of ore, perhaps even knocking as a warning of danger — hence the name 'knockers'.
'Knockers' was not the only name given to the Cornish mine spirits, though. 'Knackers', 'buccas' and 'spriggans' were also common, and in North America the term 'tommyknocker' was sometimes applied. All were varieties of fairy or pisky (the Cornish word for pixie), and as such built up quite a legendary status. A modern equivalent of the knocker could also be the Henson-inspired 'Doozer', a televisual creature that lived underground with 'Fraggles', dressed only in hard-hats and tool belts.
According to eyewitness accounts2, knockers took the form of small thin-limbed people, often dressed in the same garb as the humans who shared the mines with them. Knockers invariably had large, hooked noses, which they often picked. The habit of mining seemed to carry on to their own bodies as such and celebratory dances were held whether the yield came from the earth or nose.
While knockers generally lived underground in the tin mines, looking for ore deposits for themselves. They could also inhabit wells or other dark places like caves or rocky outcrops along the coast. Some were even said to live in trees or under the water, although it's more likely that these were different types of fairy with the same name — like 'bucca', which was often used as a generic term for any supernatural deity.
Mind Your Manners, Miner!
Knockers were thought to be benevolent beings, often warning miners of cave-ins or dangers in mines with their, well, knocking. However, they could sometimes be quite naughty, stealing tools and pinching miners' ears. This mischief could turn into rage, though, if a miner was rude, such as by whistling loudly or swearing.
The consequences could be dire, with the knockers leading a miner into dangerous areas, or even making a mineshaft collapse in on the poor unfortunate soul. And, like any fairies, they did not take too kindly to being spied upon or to someone making the sign of the cross.
Thus, to make sure that the knockers remained affable and to give thanks for warnings about cave-ins or other dangers, it became customary for miners to leave the last bite of their pasties in the mines for them.
Where Are They Now?
The origin of the knockers is probably in early Welsh mythology, with tales of sprites and 'little people' abounding. Later, the theory was that the knockers were actually the ghosts of Jews who were working the mines in penance, or were simply the spirits of souls who could not gain access to Heaven or Hell.
Regardless, the knockers have perhaps faded from memory a little now3, with the closure of many of the Cornish tin mines over time, the final mine falling silent in 1998. Just how silent, though, could be argued, as visitors to the sites sometimes claim to hear gentle knocking — and are sure to leave the last of their Cornish pasty for the knockers, just in case.