The Cwn Annwn, which means hounds of the otherworld (underworld), are Welsh phantom dogs seen as a death portent.
Their growling is louder when they are at a distance, and as they draw near the sounds grow softer and softer.

As Andrew Thomas was coming home one night, he heard, as he thought, the sound of hunting dogs.
He was afraid it was some person hunting the sheep, so he hastened on to hinder them.

He heard them coming towards him, their voices were small but increasing as they went from him.
They went down the slope towards the River Ebwy, dividing between this parish and Mynyddislwyn,
whereby he knew that they were what are called ' Cwn Wybir ' (Sky Dogs)
but in other parts of Wales, ' Cwn Annwn ' (Dogs of Hell)