Keeping the audience on the edge of their seat is the function of SUSPENSE. Suspense is not the same as action, nor is it the same as surprise. Suspense is the ANTICIPATION of action. The longer you draw out the anticipation, the greater the suspense.
Hitchcock explained; "Two men are having an innocent little chat. Let us suppose that there is a bomb underneath the table between them. Nothing happens, then all of the sudden, BOOM! There is an explosion. The audience is surprised, but prior to this surprise, it has been an absolutely ordinary scene, of no special consequence.
"Now let us take a SUSPENSE situation. The bomb is underneath the table, but the audience knows it... Probably because they have seen the villain place it there. The audience is aware that the bomb is going to explode at one O'clock, and there is a clock in the decor. It is a quarter to one. In this situation, the same innocuous conversation becomes fascinating, because the audience is longing to warn the characters on the screen: 'There's a bomb beneath you, and it's about to explode!'
"In the first case, we have given the audience fifteen seconds of SURPRISE at the moment of the explosion. In the second case, we have provided them with fifteen MINUTES of SUSPENSE."
Suspense adds spice to any scene - it doesn't have to be a thriller or action script. Comedies frequently use suspense... many of the laughs in “About A Boy” come from the anticipation that Rachel Weisz may discover that Nicholas Hoult is not really Hugh Grant's son. Every lie Hugh Grant tells is a ticking bomb that we know will eventually blow up in his face. Even though you can use suspense in comedies and dramas and musicals and romances, the most common place to use suspense is in a thriller.
“Unfaithful” takes a dramatic scene and creates suspense just by adding a weapon. Bland suburbanite Edward Sumner (Richard Gere) has discovered that his sexy wife Connie (Diane Lane) is having an affair with a hunky SoHo book dealer named Paul Martel (Olivier Martinez)... and goes to confront him. This is a dramatic situation made volatile and dangerous just by showing us a very sharp butcher's knife sitting on the table near the two men. A deadly weapon within easy reach.
SUMNER
How did you? Meet my wife?
MARTEL
By accident. On the street. There was a wind storm, she bumped into me and --
SUMNER
You're him.
MARTEL
She told you about that?
SUMNER
Yes. This is where you meet?
Martel glances at the knife.
MARTEL Yes.
SUMNER
And she likes it?
MARTEL
Well, I guess - she never complained.
SUMNER
Do you stay in all the time? Or do you go out, too?
MARTEL
It depends. Sometimes yes, we go out.
Martel moves closer to the table... and the knife.
SUMNER
MARTEL
Yes. More exciting than the suburbs, I guess.
SUMNER
We've been married eleven years. We have a son.
MARTEL
Yeah. She told me.
SUMNER
He's the reason why we left the city.
Connie thought it would be better for him.
MARTEL
Oh? She said it was your idea.
SUMNER
You talk about me?
Sumner picks up a snow globe near the bed.
SUMNER
Where did you get this?
MARTEL
It was a Gift.
Sumner twists the globe and it begins playing a music box tune.
MARTEL
SUMNER
Why would she do that?
MARTEL
Maybe she just wanted to buy me something.
SUMNER
She didn't buy it. I gave it to her. I'm feeling sick.
MARTEL
You want some water?
Sumner sits down on the bed. In his hands the snow globe keeps playing the tune.
SUMNER
I'm feeling sick. I'm not well. I'm not feeling well.
Sumner SLAMS the snow globe onto Martel's head... killing him.
Just having that knife on the table instantly creates suspense. We know that either man might grab for it at any time - and that makes the conversation exciting. Will Martel say something to set Sumner off? You think that "more exciting than the suburbs" crack is going to do it - but Sumner maintains control. That knife is right there - will Martel grab it and kill Sumner? Tension builds. We wait for someone to grab that knife. We anticipate the action - and that turns a dramatic conversation into a real edge-of-the-seat experience.
There is a great scene in “Kill Bill 2” where Uma Thurman (the bride) confronts David Carradine (Bill) as he is making sandwiches. It is a tense conversation, made *intense* by Carradine using a big shiny sharp knife to make the sandwiches - you keep waiting for him to throw it at her. This would have been a normal scene - tense, but not life threatening - if Carradine had been stirring tomato soup with a wooden spoon. No threat from the spoon. But we know what he can do with that shiny sharp knife. If Uma says or does the wrong thing - he could easily kill her. This ups the suspense... in a conversation scene.
The opening scene of the classic Private Eye movie “Murder My Sweet” has Philip Marlowe (Dick Powell) quitting work for the day, taking his gun off and putting it on his desk, then sitting back in his desk chair and looking out his office window at the city... when he sees a reflection in the window of a man standing behind him. A *huge* man. Moose Malloy (Mike Mazurki) enters the office and sits on Marlowe's desk, next to the gun, and demands that Marlowe help him find the girlfriend who he lost track of while he was in prison. Throughout the whole conversation, that gun is between the angry ex-con and Marlowe - adding tension to the scene and creating suspense. Eventually, Marlowe must carefully remove the gun without making it look threatening to Malloy... even more suspense. The great things about this scene is that it is that typical exposition-filled scene where the client hired the private eye, but with that gun on the desk between them we hardly even notice the exposition.
Tension is unresolved conflict. The conflict has to exist below the surface, and it has to threaten to erupt at any minute. When you throw a gun or a knife into the scene, the tension escalates.