Host desecration is an anti-semitic myth similar to the blood libel myth. It started in late 13th century England and France (a century after Christians started making blood libel accusations against Jews), where it was claimed that Jews would steal consecrated host wafers and torture them. According to the theory of transubstantiation, a consecrated host wafer became the flesh of Christ, so it was believed that Jews would steal and torture these wafers to reenact the crucifixion of Christ.
This myth portrayed Jews in an even worse light than the blood libels: rather than killing a mere human, they tortured what they believed to be the Messiah, a part of God Himself; if they didn't believe in both Jesus and transubstantiation, the host wafer would just be an ordinary cracker to them, so why would they go to the trouble of stealing it and stabbing it with a knife?
In some variants of the myth, the stabbed wafer bled, causing the Jew to freak out and convert. Later this variant changed to make the Jew look even worse: rather than converting in the face of this miracle, the Jew buried the wafer in an attempt to hide it; where the wafer was buried, a new spring burst forth from the ground. Regardless of the variation, many Jews were killed because of this myth until it started to wane with the advent of Protestantism.
Host desecration forms part of myths about devil worship, particularly the black mass, both in medieval times and later in allegations of satanic ritual abuse.
