Romanian witchcraft is (not surprisingly given the religiosity of the country) rooted in Christianity, which in its turn copied the principles of a blood sacrifice and scapegoating from Judaism. Christianity and Judaism are strongly influenced by principles of blood magic.
Middle Eastern ancient religions quite often demanded bloodshed to mollify the gods. Crimes against humanity were punishable by death, so naturally sins against the gods demanded something be killed to make things better. Judaism is no exception.
In Genesis 4, Cain and Abel are the first human beings to offer God offerings. God prefers Abel’s offering of dead animal parts with favor but looks on Cain’s offerings of vegetable matter not-so-favorably. From that supposed first blood offering stem dozens of blood offerings and the scapegoat principle found in the OT, including human sacrifice. The most extensive accounts of child sacrifice in the Hebrew Bible refer to those carried out in Gehenna by two kings of Judah, Ahaz and Manasseh of Judah.
Christianity simply altered the process to make it less barbaric and more easily adaptable: one single human (scapegoat) sacrifice covered all sins in perpetuity…so long as you continue to observe the ceremonial meal which in effect reenacts the sacrifice every time you perform it.
It's mainly Paul who constructed this reinterpretation of an ancient notion. Paul had already taken circumcision, the central identity marker of the Jewish faith, and had declared that true circumcision is a metaphorical removal of wickedness from the heart. There’s way less bloodshed, this way. Someone had also already reinterpreted the Passover meal to signify the bloody death of Jesus by Paul's time.
Towards the end of the Middle Ages and the beginning of the early modern period (post-Reformation), belief in witchcraft became more popular and witches were seen as directly in league with the Devil. It is therefore not surprising that blood offerings turn up the period's Christianized versions of witchcraft. It is the price paid for warding off the demonic "soul price' that Christianity associated with magic. This is a direct parallel with the crucifixion, during which the Nazarene was also said to be tempted by the devil.
The soul of course being a concept that is very different in the original pagan thought. The animistic aspects of Pagan theology assert that all things have a soul - not just humans or organic life - so this bond is held with mountains and rivers as well as trees and wild animals.