The painting above by Tivadar Kosztka Csontváry has a pretty amazing secret to it which can be seen by using a mirror.
If you place the mirror exactly in the middle of the painting, on the left, you can see a man — wise-looking and sad — resting with his back to the serene mountains and the calm sea. He is God.
If you look to the right, you will see a man — evil-looking and menacing — with his back to the erupting volcano and the stormy sea. He is the Devil.