In fact, pagan rituals often drank the blood of animals that were sacrificed because they superstitiously believed that the life force became a part of them. It could extend their own life. Conquering leaders sometimes drank the blood of the defeated kings because they believed that their power and life would literally become their own.
Hebrews believed in the power of blood when making covenants. A covenant as seen with Abram literally means the way of the blood. It signifies the agreement that if either party breaks the conditions then each one expects their blood to be poured out as payment. It was messy. It was gory.