Among Slavic accounts of the soul, references to people who have two souls occur relatively often; having two souls is usually regarded as a demonic and dangerous trait, characteristic of people who are demons. In the beliefs of Carpathian Ukrainians and Poles, “two-souled people” are credited with the ability to control hail clouds and torrential rains: while they sleep, one of their souls remains in the body, while the other, demonic one, leaves the body and goes to fight the cloud; after driving it away, it returns to the sleeping body. (...) After death, those with two souls become dangerous demons—vampires, atmospheric demons, and so on. Pregnant women are often believed to have two souls.

S. M. Tolstaya, “Slavic Mythological Ideas about the Soul,” 2000.