In Christianity, a Eucharistic miracle is any miracle involving the Eucharist. In the Roman Catholic, Lutheran, Eastern Orthodox, Methodist, Anglican and Oriental Orthodox Churches, the fact that Christ is really made manifest in the Eucharist is correctly deemed a Eucharistic miracle; however, this is to be distinguished from other manifestations of God. In general, reported Eucharistic miracles usually consist of unexplainable phenomenon such as consecrated Hosts visibly transforming into myocardium tissue, being preserved for extremely long stretches of time, surviving being thrown into fire, bleeding, or even sustaining people for decades. Verification of Eucharistic miracles often depends on the religious branch reporting the supposed miracle, but in the case of the Catholic Church, a special task-force or commission investigates supposed Eucharistic miracles before deciding whether they are "worthy of belief." As with other miracles, such as Marian apparitions, belief in approved miracles is not mandated by the Catholic Church, but often serves to reassure believers of God's presence or as the means to "send a message" to the population at large. Anglican Churches have also confirmed extraordinary Eucharistic miracles. It is also not uncommon for religious authorities to allow secular sources to investigate, and verify, at least specifics (such as muscle type) of the supposed miracle.​
 

https://en.wikipedia.org/wiki/Eucharistic_miracle