“Another fascinating example of esoteric knowledge adopted by the informed to communicate secretly was the use of sign language for the deaf. Unknown to most people today, Renaissance Italian artists had no difficulties working with their hearing-impaired friends and colleagues. Even today, especially in southern Italy, there is a deeply engrained tradition of expressing oneself through nonverbal communication, using hand gestures, facial expressions, and body language in general. Leonardo da Vinci, in his day, encouraged other hearing artists to learn from the expressivity of the deaf.”