Modern technology has allowed scientists to see 'through' the paint of Leonardo da Vinci’s 'Mona Lisa.' In 2004, a specialized multi-spectral camera discovered three distinct versions of the painting beneath the one we see today. One hidden layer shows a woman with a larger head and hands, and another shows a woman wearing a pearl headdress. These findings suggest that Leonardo worked on the portrait for over a decade, constantly revising and painting over his previous work. This technique, known as 'pentimento' (from the Italian word for repentance), shows the artist changing his mind. These hidden layers provide a rare glimpse into the perfectionist nature of Leonardo and the long evolution of the world's most famous smile.