Leonardo Da Vinci's 'The Last Supper' reveals more secrets

"We asked ourselves why Da Vinci chose those particular foods, because they don't correspond to what the Evangelists described," says Bauer. "Why bread, fish, salt, citrus and wine? Why is the saltshaker tipped over in front of Judas? Why is the bread leavened?"

The four researchers don't buy into the farfetched hypotheses introduced by Dan Brown in his best-selling book, The Da Vinci Code, yet they agree the artist included symbols and commentary in his depiction. He purposely attempted to confuse and fool the observer with contradictory symbols and double-meanings.

For instance, a fallen saltshaker is traditionally a sign of bad luck. The researchers question if instead of indicating the mischief of Judas, the fallen saltshaker could suggest his rehabilitation. He could have been chosen to play the role of the traitor. And why is he the only one with an empty plate? It could mean he is full and mischievous or that he is the only one who isn't fooled?

The fish has also been the topic of several studies. It is clearly a reminder that Jesus spent most of his life around Lake Tiberias and that he selected his Apostles among local fishermen. Yet it isn't clear whether the fish is herring or eel. Some argue Da Vinci was deliberately ambiguous about the species of fish. Eel in Italian is aringa, although when it is spelled arringa it means indoctrination. And herring in northern Italy is renga, meaning he who denies religion.

The painting continues to fascinate and mystify. Its restoration, which took place between 1979 and 1999, has brought to light new details that along with new technology has spurred a new wave of research and interpretation of one of the world's most famous artworks.