In Bulgaria when a child who was born on a Saturday dies without having been baptized, then nine days after its burial, it rises from its grave as a type of vampire known as an ustrel (“lost heart”). Almost immediately after it begins its unlife, the ustrel begins to look for cattle upon whose blood it will feed, sometimes up to five a night, and then return to its grave. After ten days of feeding, if it has managed not to get itself killed by a hired VAMPIRDZHIJA, the ustrel will no longer need to return to its grave at night but rather will live, invisibly, in the place between the horns of a cow or ram. This is the perfect place for it to live, as it is hated by wolves that will tear it apart if they can. Roosting atop a cow offers it protection, as humans are likely to prevent wolves from entering into their herds for fear that they are there to hunt and kill their livestock.

Source: Bryant, Handbook of Death, 99; Frazer, Leaves from the Golden Bough, 37; Keyworth, Troublesome Corpses, 68