It was once customary to hold vigil when someone died to make sure that the dearly departed was not disturbed in their eternal rest. This practice was likely a relic of the ancient belief that if an animal or human passes over a corpse it will re-animate into a vampire or some other type of undead. The belief holds that if some living thing moves over the cadaver, it will snatch just enough life force to return from the undead. The belief is widespread and can be found in many places throughout the world.
From Eastern Europe to China it was considered unlucky for an animal, such as a cat, to jump over the corpse. The most likely culprits are dogs and cats, but birds, bats, and certain insects were also seen as guilty parties in bringing back the dead.
In Romania a black rooster was considered most likely to jump-start the un-life of a corpse. But in the Russian Steppes it wasn’t always a living thing that would create a vampire. In many Russian villages it was believed that to pass a candle over the body would resurrect it as a vampire. (Candlelight was seen as a living force). Wind blowing over the corpse was also seen as dangerous.
In many parts of Europe it was customary to leave windows and doors open as long as the corpse was housed there, so that the person’s soul might escape. But this created the potential that some animal might get in and jump over the corpse. Thus, someone was assigned to stay with the corpse to keep its rest from being disturbed. In most folklore, vampires were usually created from their rest being disturbed or if the corpse was not given a proper burial.