Religion needs miracles. Miracles prove to the faithful that the deity they believe in does indeed exist and interact with them. Miracles show that praying works. And last but not least, miracles are what you have to accrue if you want to move up the ladder in the Catholic undead hierarchy after you die.
One such miracle was long said to have happened in Bolsena, Italy in the year 1263, and it was quite an important one too, in that it spawned the feast of Corpus Christi, and seemed to affirm the Catholic doctrine of transsubstantiation, you know, the whole “cracker and wine turn into the flesh of some undead jewish zombie when mumbled upon in Latin by a guy in red robes” thing. What happened in Bolsena was this :
In 1263 a German priest, Peter of Prague, stopped at Bolsena while on a pilgrimage to Rome. He is described as being a pious priest, but one who found it difficult to believe that Christ was actually present in the consecrated Host. While celebrating Holy Mass above the tomb of St. Christina (located in the church named for this martyr), he had barely spoken the words of Consecration when blood started to seep from the consecrated Host and trickle over his hands onto the altar and the corporal.
The priest was immediately confused. At first he attempted to hide the blood, but then he interrupted the Mass and asked to be taken to the neighboring city of Orvieto, the city where Pope Ur ban IV was then residing.
The Pope listened to the priest’s account and absolved him. He then sent emissaries for an immediate investigation. When all the facts were ascertained, he ordered the Bishop of the diocese to bring to Orvieto the Host and the linen cloth bearing the stains of blood. With archbishops, cardinals and other Church dignitaries in attendance, the Pope met the procession and, amid great pomp, had the relics placed in the cathedral. The linen corporal bearing the spots of blood is still reverently enshrined and exhibited in the Cathedral of Orvieto.
The scene was depicted by Raphael :
There are no miracles.The laws of nature do not get suspended. Underlying all claims of miracles is the fact that they are not scientifically testable events, and hence require a healthy injection of faith and confirmation bias. We humans don’t know everything, and there will always be events that we can not explain with the knowledge about the world that we have at the time. Just like with the Miracle of Bolsena and the bleeding cracker :
Throughout history, the unexplained appearances of “blood” on food were perceived, by the superstitious and the credulous, as miracles or as portents of evil. However, experiments by various scientists suggest a natural rather than a metaphysical explanation. Prodigiosin-producing Serratia marcescens is currently thought to be the cause of the miraculous blood.
The most famous of the miracles attributed to S. marcescens is the Miracle of Bolsena in the 13th century.  The earliest recognition that blood on food may be a natural phenomenon occurred in the 19th century in Savonara, Italy, when Father Pietro Melo was asked to exorcise a house with bloody polenta. Although Melo was a priest, he also had a Ph.D. in botany. He believed in a natural rather than a miraculous explanation for the bloody cornmeal. For a thorough account of the transition from superstition to the evolution of scientific thought on S. marcescens and bloody food, read Gaughran (1969).
In the last decade, microbiologists have grown S. marscecens to simulate the incidents in Bolsena and Savonara. Dr. Joan Bennet and her students grew S. marcescens on Manischewitz Passover matzos and on unconsecrated wafers from the Episcopalian and Roman Catholic churches. The Protestant wafers produced growth that most resembles blood (1). Johanna Cullen cultivated S. marcescens on polenta and sacramental bread in the laboratory and produced similar bloodlike growth (2). This circumstantial evidence is consistent with the notion that the Miracle of Bolsena and other such incidents were simply a manifestation of microbial growth.
We humans are pattern-seeking creatures. Religious believers think that the laws of nature get suspended every now and then to heal some random lucky person from Parkinson’s disease or Leukemia, or to make inanimate matter bleed. As Thibault once remarked, there are lots of crutches on the walls in the grotto at Lourdes, but no wooden legs. Things have natural explanations, the laws of Physics don’t change at a whim just to affirm middle eastern stone age dogma. The fact that we don’t have a natural explanation for a given event yet does not mean that there isn’t one. It makes the believers look ridiculous and credulous when they attempt to shove their god into every vaguely unexplained natural phenomenon. But it sure is a time-honored tradition.