What's the greatest hook in the world?

?

Emotional hook.  Relationship hook.

A question.

What's a question mark look like?   ON ITS SIDE.
UPSIDE DOWN ¿

On the surface, it's the tools used in the story that hook the audience.  The tools are what we showcase in a movie trailer.

But underneath, it's the theme, it's that question the story sets up, that lingers in the back of your mind, that hooks you.