There is a distinct difference between “suspense” and “surprise”, and yet many pictures continually confuse the two. We are now having a very innocent little chat. Let us suppose that there is a bomb underneath this table between us. Nothing happens and then all of a sudden: Boom! There is an explosion. The public is surprised, but prior to this surprise, it has seen an absolutely ordinary scene, of no special consequence. Now let us take a suspense situation. The bomb is underneath the table and the public knows it. The public is aware that the bomb is going to explode at one o’clock and there is a clock in the decor. The public can see that it is a quarter to one. In these conditions the same innocuous conversation becomes fascinating because the public is participating in the scene.
(c) Hitchock by Francois Truffaut