In folklore, there are phantom black dogs that roam through graveyards and patrol boundaries like roads and footpaths. Large and shaggy, with glowing red eyes, these ghost dogs may appear just prior to a death. Some say that if they look directly at you, you will die. In other myths, they appear to play the role of protector, for example, of the souls of the dead buried in a graveyard.
A myth dating from August 4, 1577, tells of a black dog appearing during a thunderstorm in a church in Bungay, Suffolk, killing two people and injuring a third. The same day, a similar black dog appeared in a church in nearby Blythburgh and people died there as well. Bob Trubshaw summarizes a number of folkloric accounts of black dogs, and another interesting website specifically on the August 4 events is at everything2.
Our black dog is medium sized, has brown eyes rather than red ones, and is merely high strung -- not ghostly and ominous. She's not a hell hound, just a brat.