Mystery of the Mona Lisa's smile solved !
Da Vinci's notes from 1478 to 1519 are known as the Codex Atlanticus; over one thousand pages of his thoughts and sketches on flight, musical instruments, weapons of war, botany and maths amongst other things.
Bound into twelve-volumes, and originally gathered together by the sculptor Pompeo Leoni in the late 16th century, the Codex underwent restoration in 1974 and this sketch was discovered ...
Alas, after much debate and investigation, in 1997 this page was proven to be a 20th century forgery. The Codex is currently preserved at the Biblioteca Ambrosiana in Milan.
Eh, who's to say da Vinci didn't invent a cycle-like contraption. His notebooks were physically ripped apart to be be bound into the Codex, who's to say Pompeo Leoni didn't indulge in some "editing" and lose a few pages in the process.
I choose to believe.