Blech finds it another hidden message. "I think this is one of these powerful proofs, that not only did Michelangelo know Jewish texts, but he felt it important to incorporate the ideas of these texts into some of these frescoes."
Vatican Curator Nesselrath dismisses the Kabbalah references. "Well, we have all to remember that this is the palace chapel, the main chapel of the Vatican palace, and whatever Michelangelo is painting here had to be discussed with the Pope and his advisors."
And about that Pope — the authors of "The Sistine Secrets" claim that Michelangelo was furious at Julius II, who commissioned the work. Michelangelo was a sculptor, not a painter, and was angry to put his sculpture career on hold to paint frescoes. They say that anger caused the artist to paint hidden references on the ceiling to the corruption of the papacy of his time.
"All these things upset Michelangelo very much. My own personal feeling is that Michelangelo had to get this off his chest," Blech explained.
Just how badly behaved were the Popes of the Renaissance?
"There isn't a Renaissance Pope that didn't father plenty of children, and Alexander the Sixth had children — but this was well known," noted Michelangelo scholar professor William Wallace says.
Monsignor Timothy Verdon of Florence concurs, but can't imagine that Michelangelo gave it any thought. "Italians always understood that these men were human. If in their youth there had been a mistress or two, if there were illegitimate children, this was not really all that surprising. If the Pope went out of his way to favor his nephews … it was considered good policy … It's a bit hard to think that Michelangelo could have been deeply concerned with great questions of church reform."
But the authors contend that there are insults hidden in plain sight — right above the place where the Papal throne would sit. They point out the fresco of the Prophet Zachariah, directly above the Pope's seat. They say it's actually a portrait of the Pope himself.
"This is actually Julius II," said Blech. "Behind him, are little 'putti,' little angels. And this perhaps is the key to understanding Michelangelo's courage, Michelangelo's true feelings about the Pope, and the fact that Michelangelo did not hesitate to present us with messages that might've been offensive."
He says one of the putti is doing the Renaissance equivalent of giving the Pope's portrait "the finger."
"There's no doubt about it," he says, "this little putti, this beautiful little angel, is giving the finger not to Zachariah, but to Pope Julius."
He says the ceiling is full of insults, and that the hand gesture is seen again in the fresco of the Cumaean Sibyl.
"It happens a second time … Twice, that's a statement."
On Friday May 2 at 8 p.m. ET, ABC News anchor Martin Bashir travels to Florence and Rome and talks to to renowned Michelangelo scholars and theologians to find out if the authors' remarkable claims are true.