Check out this puzzle of mine as well.

You’re a Cthulhu cultist and believe that Cthulhu will reward you by eating you first iff you perform painful ritual self-mutilation in His honor when the moon is full and would do so even if you believed that Cthulhu does not exist. You know, of course, that Cthulhu is a perfect predictor of mortals’ actions, so He knows what you would do.

One day you’re persuaded by an atheist’s arguments that Cthulhu doesn’t actually exist.

That night the moon is full. Do you perform the ritual?