There’s a great scene with a gigantic snake in Conan the Barbarian. Originally, the script called for Conan to drip sweat on the snake, which makes it open its eyes.
Being a reptile enthusiast, I approached writer-director John Milius.
“There’s a problem with this scene, John.”
“What is it?”
“Snakes don’t have eyelids — but here’s what we can do: When Conan drips sweat onto the snake, have the snake’s pupils dilate, to show its been awoken from its slumber.”
And that’s what we did.
Moral (from the Unwritten Rules of Hollywood): Never present a problem unless you already have the solution.