Calan Gaeaf is the name of the first day of winter in Wales, observed on 1 November. The night before is Nos Galan Gaeaf or Noson Galan Gaeaf, an Ysbrydnos ("spirit night") when spirits are abroad. Traditionally, people avoid churchyards, stiles, and crossroads, since spirits are thought to gather there.
Villagers would dance around a bonfire and everyone would write their names on, or otherwise mark, rocks and place them in and around said fire. When the fire started to die out, they would all run home, believing if they stayed, Yr Hwch Ddu Gwta (a bad omen that took the form of a tailless black sow with a headless woman) or Y Ladi Wen ("the white lady", a ghostly apparition often said to be headless) would chase them or devour their souls.
One particular rhyme shows how the last child out on Nos Calan Gaeaf was at risk of being eaten by the fearsome beast:
|Adref, adref, am y cyntaf',
Hwch ddu gwta a gipio'r ola'.
|Home, home, at once|
The tailless black sow shall snatch the last [one].
The following morning, all the stones containing villagers' names would be checked, and finding one's stone burned clean was believed to be good luck. If, however, a stone was missing, the person who wrote their name on the absent stone would be believed to die within one year.