A lovely article mentions that:
superimposing the Last Supper with its mirror-image throws up another picture containing a figure who looks like a Templar knight and another holding a small baby.
Excited by this finding, I looked for more. I could not find much in the Mona Lisa:
But indeed the Vitruvian Man after superimposing a mirror image shows incredibly large balls:
Leonardo was Italian, and in Italy "growing big balls" means "getting very tired and sick of something". This is clearly a very deep message from Leonardo.
But why stop at Lenoardo?