It's not our faces that tend to offer the strongest clues about what we are feeling, but rather our bodies. In fact, the more intense the emotion, the more difficult the human face becomes to read and the more telling and accurate body language seems to become. That's what a team of Princeton University researchers found in a study published in the journal Science all the way back in 2013.

So, we checked in with two experts to help us decode some of each presidential candidate's most common body language in high-stress moments. Both experts reviewed the photos below via email, without the photo captions. We've edited their comments for clarity and length. We put a special emphasis on identifying each of the candidates' most common body language, particularly in stressful situations.

For this reason, A Washington Post team brought in body language experts to offer live, during the debate analysis of each candidate's body language. And, The Fix talked to two experts before the debate to create the following basic guide for debate viewers.

The experts

David Givens is the director of the Center for Non-Verbal Studies, a nonprofit research center in Spokane, Wash. Givens's research focuses on body movement, gestures, facial expressions, adornment and fashion, architecture, mass media and consumer-product design.

Ruth Sherman is a political communications consultant, coach and former faculty member at the Yale University Women's Campaign School. She has advised candidates and business leaders on public speaking, debate performance and other forms of communication for decades.

Example One -- Go-to Hand Gestures

GIVENS: Politicians may soften the impact of an aggressively fisted gesture [or aggressive point] by placing the thumb's fleshy, rounded tactile pad atop the fist's flexed index finger. In the Lincoln Memorial in Washington, D.C., the 1922 sculpture of a seated Abraham Lincoln by sculptor Daniel French featured the president's fleshy thumbs to humanize the monumental 19-foot-high, 120-ton statue.

In the same way, the thumb-over-fist gesture, first used by President John F. Kennedy in the 1960s, became a cue used to emphasize speaking points without seeming to be overly aggressive in the process. After Kennedy, numerous U.S. politicians, including Presidents Bill Clinton and Barack Obama, used [it] to show strength, to humanize their political speeches, and to disarm and connect emotionally with voters.

SHERMAN: I think she just picked this up from Bill [Clinton]. It's her go-to emphatic gesture, when she's trying to make an important point.

She'd be much better off if she didn't use it because of what it reminds us of. This is the gesture [Bill] Clinton used that reminds us of the famous line, "I did not have sex with that woman." It's [also] a closed gesture indicating some leakage of tenseness and/or insecurity. Opening her hands would look better and convey a more open, confident posture.

SHERMAN: The most common Trump gesture. Sometimes he mirrors with his other hand and other times, only his right is engaged. This gesture seems to be Trump's favorite when he's riffing on an idea or when he wants to emphasize a point.

Example Two -- Watch The Gaze 

GIVENS: Bowing or tilting the head forward so that the eyes face the ground or floor may convey a defeated attitude. It may also reflect guilt, shame or submissiveness, as when distorting the truth or telling a lie. Gazing down while -- or shortly after -- stating "I am innocent," e.g., shows that a speaker may not believe his or her own remarks. True statements are normally given with a confident face-to-face or level gaze, which may be held longer than three seconds.

Example Three - Those Hands and Arms Can Say a Lot

GIVENS: Identified by Charles Darwin in 1872, the shoulder shrug is an interrelated set of 13 body motions, from the head to the toes, used worldwide to show helplessness, resignation and uncertainty. The shoulder-shrug display involves the entire body in a visual crouch.

GIVENS: Throughout the world, palm-up cues reflect moods of congeniality, humility and uncertainty. (Palm-up gestures contrast with palm-down cues, which are more domineering and assertive-like in tone.) Accompanied by "palm shows," our ideas, opinions and remarks may seem patronizing or conciliatory, rather than aggressive or "pointed." Held out to an opponent across a conference table, the palm-up cue may like an olive branch, enlisting support as an emblem of peace. Held out to viewers, Trump welcomes and draws them emotionally closer.

GIVENS: Donald often uses aggressive, finger-pointing gestures when he speaks. Finger pointing is universally discouraged around the world, as it focuses too much attention on a viewer. Pointed fingers, like pointed bones, are often used in sorcery to cast an evil spell. Pointing associates well with anger, and certainly does so in Donald’s case.

SHERMAN: Is this the "my African American" thing?  Of course it looks like he's pointing a gun, which would be big time leakage, but he might have just come out of his "A-okay" gesture. We cannot ignore the hat, either, as dress and adornment are nonverbal codes. If it's outdoors, he has to keep his hair in place, and I do honestly think he created the cap merchandise first for this reason. [This] goes to his vanity in the topic.

GIVENS: An insistent speaking or listening cue made with the fingers extended and the hand(s) rotated to a downward (or pronated) position. A posture in which the hands and forearms assume the prone position used in a floor pushup. While speaking, palm-down gestures show confidence, assertiveness and dominance. (Palm-down gestures contrast with the friendlier, and more conciliatory, palm-up cue.) Accompanied by aggressive, palm-down "beating" signs, our ideas, opinions and remarks appear stronger and more convincing.

SHERMAN: This -- the accordion -- is his second most common gesture. He often brings the hands together and apart rapidly to add emphasis or when he's wondering aloud about why something hasn't been done or what something is happening that he thinks should not be. He'll often move from this one to a shoulder shrug with palms facing up. This seems to convey an impatience and resistance to being overpowered or even argued with by the conversation partner. Notice, too, how his elbows are [sitting] tightly against his torso. This is a protective stance and also leaks insecurity.

That should be enough to help voters navigate the unspoken language of Sunday night's debate.