Transubstantiation

Transubstantiation is a cannibalistic idea pronounced by Thomas Aquinas that the consecrated Eucharistic bread and wine undergoes a miraculous transformation into the actual flesh and blood of Jesus Christ at the point of consumption by the members of the congregation who accept communion.

It has been said that this is based upon an analysis by Aristotle of the nature of matter.

Transubstantiation is the current belief of the Roman Catholic Church but they do not seem to consider it as cannibalistic, which eating the flesh of a once living human being should be considered. 

Even most Protestants consider communion to be at least symbolic of the eating and drinking of the flesh and blood of Jesus Christ, which probably should be considered as symbolic cannibalism.

A strange concept to be sure!

The actual eating of one's God is called Theophagy.