Why are Reaction Shots Important?

Reaction shot is a shot which cuts away from the main scene in order to show the reaction of a character to it.

That’s it in a nutshell.  A reaction shot is usually silent, as it shows a character reacting with facial expressions (a frown, a smile, a gasp).  Sometimes a shot starts with a silent reaction before the character vocalizes his emotions.

To illustrate: if the main conflict of a scene is a married couple arguing, a potential reaction shot could be the kids watching, visibly worried. In fact:

This is the reaction of a daughter, eavesdropping from the stairwell, as her mother tells her husband she wants a divorce. From Mrs. Doubtfire (1993).

More often than not, reaction shots are a close-up or a tight medium because that proximity allows the audience to see the reaction up close, and thus connect to the character.

This is a clip from Indecent Proposal (1993) where billionaire John Gage (Robert Redford) makes an unsettling offer to a couple he just met:

The beauty of reaction shots is that they are subtle. The inattentive viewer doesn’t think, “Hey, there’s a reaction shot, now another…” More often than not, we just absorb the emotion, “Wow, Demi Moore was outraged. Was she crying? I think I saw tears.”

But when you step back to analyze the construction of the scene, you can see how it was directed and cut for impact. In fact, watch that scene again on mute, and it should become even more obvious how the mechanics works.

Now that you have seen a couple of examples, let’s examine why reaction shots are so important to the medium:

Purposes of Reaction Shots

Here’s Brad Pitt’s character blackmailed. His choices: go into zombie land by himself or with his family. From World War Z (2013)

1. For Story

As the name implies, a reaction shot contains someone’s reaction, which is a quick emotional beat. Above you have a reaction shot from World War Z. Without the context, you can still tell that Brad Pitt is not pleased, maybe he’s even confused. This quick reaction shot is enough to convey his feelings. If you watch it in context, that shot will make even more sense and thus be more powerful. Also, lips quivering and veins pulsating make for great reactions.

2. For Editors

Editor loves reaction shots because it gives them flexibility and choices.

For example, imagine this unlikely scenario:

Suppose that the camera operator captured two takes of an actor’s speech, both of which lasted 1 minute long. Now imagine that the first half of the actor’s speech is more powerful in the first take, while the second half is stronger in the second take. Without another character’s reaction (or another cutaway), the editor only has two choices: take 1 or take 2. However, with the reaction shot of a secondary character, the editor has a third choice: he can bridge the first take and the second take by cutting away to the reaction shot during the transition from one take to the other.

3. For Performance

Imagine if there was a device that allowed you to point to a person and know what they are feeling at a specific moment. Well, in this art, such device exists, and it’s called the camera. When you point it to someone responding to something, you can get a glimpse of what they are feeling. And this puts the actor’s in a great position to showcase his performance, which also advances the story.

Source: http://www.elementsofcinema.com/editing/what-is-a-reaction-shot-in-movies/