Naples Cathedral is easily the worst cathedral I have visited, and I have been to very many all over Europe. It is located in a run-down and overcrowded slum just north of the dock area and was actually locked when we tried to go in last year.
Perhaps this was to protect the treasures inside from the surrounding poor in the crime capital of Europe where the devout Catholic inhabitants will steal anything that isn't bolted down, only to have their sin counter reset in confession on Sunday. Meanwhile, the rubbish piles up in the streets and bins remain unemptied because the organised crime syndicates who run the collection service haven't had a big enough bribe this month. Maybe the inside of the cathedral is better than the grim facade, but if this is the best San Gennaro can do by way of protecting the city he loves, he's a sorry excuse for a patron saint.
Occasionally, due to rough handling when carrying the bottle of 'blood' from its safe keeping place, locked away from prying and sceptical eyes, in the crypt of the Cathedral, the blood will already have liquified before a pope or bishop gets anywhere near it. On these occasions, San Gennaro is declared to have been so keen to show his love for the city that he started the miracle early, presumably in an example of premature liquefaction such as we might expect of a celibate saint. There's always a sensible explanation for these things.
Often, failure to 'liquify' is followed in the coming weeks or months by an earthquake, which happen frequently and unrelated to whether the 'miracle' occurred or not, in this part of Italy which is so seismically active that the western suburb of Naples is called Fuorigrotta, or 'smoking field'. This earthquake will be presented as evidence that San Gennaro had withdrawn his love and Neapolitans should give more money to the Church. When earthquakes happen anyway, this is definitely not a sign from San Gennaro at all... got that!?
So, the blood can turn liquid on it's own, or when handled by a pope or a bishop, or not turn liquid at all, and these are all miraculous signs from San Gennaro - and they all mean give more money to the Church. Isn't religion marvelous!
As B.F.Skinner showed, you can get the same effect with operant conditioning of pigeons when you randomly give a reward, dissociated from the pigeon's actions. They also become religious and perform random and pointless rituals, apparently ascribing success to their actions and failure to their own failures in not performing the actions correctly.
If you want to perform this 'miracle' for yourself, all you need is a glass bottle partly filled with a brownish substance called iron chloride mixed with calcium carbonate and salt. Apart from the bottle, all these things can be found near Naples, especially around Vesuvius and Fuorigrotta. It can even look quite like you would imagine nearly 1700 year old dried blood to look like. When you shake the bottle, however, it becomes quite liquid for a while until it settles back into the dried powder. With any luck you should be able to find some credulous and gullible people to fool but generally it works best when done by someone whom the people have been conditioned to believe already have magic powers anyway.
Just as with his veneration of the obviously fake Shroud of Turin which attracts visitors from all over the world to
Honest Uncle Frankie, the 'reforming' people's Pope, is not the least concerned about using the tactics of the snake-oil seller, the faith healer and the confidence trickster to keep the wool between their ears pulled over the eyes of the Catholic Church's victims. After all, who's bothered about honesty and integrity when there's money to be made and privileges for clerics to be defended?