Leonardo da Vinci's Milan

Every morning, going back to his painting, Leonardo sees that the snake from the Sforza family’s coat of arms (a special design used as a symbol of their identity) has been removed: he always draws it again, afraid his patrons will soon visit his artwork.

One night, waiting in the dark to unveil the mystery, Leonardo catches the Devil removing the painted snake. The Devil claims that Leonardo can’t have one of the Devil’s symbols above Christ’s hand: 

“If your student can solve many a riddle, I will be painted up the fresco in the very middle, otherwise your work I will destroy and no more colour you will enjoy”.