When writing, we can use a variety of tools to convey the information in a scene. “The ball is blue.” Tells us the color of the ball. “‘The ball is blue,’ Jeff said with revulsion.” Tells us the color of the ball as well as telling us (rather inelegantly) Jeff’s opinion of the ball’s color.
There is plenty of human emotion, reaction, and interaction that is conveyed nonverbally, and there’s a value in trying to weave in body language and other nonverbal communication to change the scene from a tell (“with revulsion”) to a show (“as he stepped back, arms crossed”).
To borrow from a much more effective teacher, Mary Robinette Kowal, as she put it on Writing Excuses in Season 11, Episode 43, from their transcripts page with minor editing denoted by ellipses in brackets:
[Brandon] All right. So, question. Amy asks, “Do you have any tips for writing body language that reveals a character’s internal state?”
[Mary] There are three different basic types of movement. Aggressive, passive, and regressive. Aggressive movement is anything that you want to engage with further. So anything that you lean in towards. You step towards, you turn towards. This is happiness, curiosity, certain types of anger. Passive is something you don’t have strong feelings about. You stay more or less in the same spot. Regressive is anything you do not want to engage with. So revulsion, fear, again certain types of anger. That’s a movement away from. So a step back, a turn, a lean. So there’s a difference between the training phrase “What did you say?” “What did you say?” She leaned across the table. “What did you say?” She pushed back from the table. So this is a very simple piece of body language that we are used to doing, to reading all by ourselves, normally. The other piece of body language, and again, it works just the same way on stage as it does on paper, is open or closed silhouette. So arms crossed is, again, something you don’t want to engage with. Cold, even though we’re talking about a temperature, you don’t want to engage with that. It’s still a closed body movement. Fear. Often these will be closed. Open body language, arms out, again things you want to engage with. So. “Hello.” She spread her arms. “Hello.” She crossed her arms. Those are things that your readers will know how to interpret. So that’s one thing is the kind of body language that you use. The other piece of that is your point of view character’s interpretation of these things. Their own emotional response to it will cue your readers. Okay. That was me with my compressed thing.
This is brilliant stuff. It’s brilliant in no small part because it ought to be obvious. We communicate nonverbally and interpret nonverbal communication every single day and somehow this is not second nature when writing (at least, not for me).
One more piece of wisdom from Tananarive Due:
[Tananarive] One quick warning. I would say to writers, don’t overuse those gestures, especially from the point of view character. It’s great if your point of view character is noticing gestures, but we don’t… We’re not often aware of the gestures we’re making. So the ear tugging and nose scratching and all those sorts of things sometimes serve as a substitute for their internal emotional process that would be better served by just saying what they’re feeling, or their stomach is cramping.
This is another spectacular point, and one that in a way refers back to filtering words and being cognizant of the POV through which the reader experiences the story.