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The mouth of Truth

The Truth About Lie Detection in Ancient and Modern Times

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Humans have told truths and lies throughout all of history. We stretch the truth for various reasons. We sometimes spin little white lies of convenience, and big, catastrophic lies that shake civilizations. We lie in order to avoid consequences, humiliation, and to please others. As a matter of survival it’s been important to tell lies from truth, and since the dawn of time we’ve sought ways to know the difference. So without our modern neurological sensory equipment and advanced interrogation techniques, how did the ancients determine if someone was fibbing?

Approaches employed in determining truth or lies depended much on religious and cultural background. A common sense understanding of the world, and practical experience, were the early tools of lie detection. Evidence was almost always based on sworn oaths and testimony. This was so until the introduction of more objective techniques, such as measurement, forensics, and the scientific method were employed by Archimedes, and during the Scientific Revolution centuries later.

Observing and judging a person’s behaviour, facial expression, and speech was, and remains today, one of the ways of discerning guilt from innocence, and deciding whether someone is lying. Lacking objective techniques, trial by ordeal was often applied in antiquity, testing unfortunate suspects in confounding and sometimes violent ways.

Rice and Donkeys

In ancient China, a suspect would be made to chew dry rice while being questioned. When the suspect spat out the rice, they were assumed to be guilty if the grains remained stuck to their tongue. The reasoning was that the stress created by lying would slow saliva flow and cause a dry mouth. It was believed an innocent person would have no reason to stress under such conditions.

In 500 BC, priests of ancient India would suss out thieves by sooting the tails of donkeys and putting them in dark tents. The suspected thieves were advised to enter the tent and pull the tail of the donkey. If the donkey brayed, the accused’s guilt would be confirmed. If the accused left the tent with clean hands free of soot, the priests would know he had not pulled the donkey tail out of fear of being revealed a thief.

The Mouth of Truth

In Rome a 2,200 year old, giant marble head waits to reveal liars and trickery.

The Bocca della Verità (the Mouth of Truth) is a heavy marble disc carved into the shape of a head and face. It is said to originally represent the Titan god Oceanus, of the great earth-encircling river which feeds all the world’s rivers, wells, and springs. Beginning in the middle ages the disc was supposed to tell truth from lies. Where the Bocca della Verità sits, at the Church of Santa Maria in Rome, has become a place where one can take the ‘test of truth’. RetroBlogRome writes of the old Roman legend, “obliging the one who takes an oath to put his hand in the Bocca della Verità. If they were not telling the truth the hand could not withdraw and was removed with a violent bite of the mouth.”

To this day the giant marble face still judges those who wish to take the test of truth by daring to place their hands in its mouth.

Trial by Ordeal

Trials by ordeal were a common means of detecting guilt from innocence, although they’re widely considered now to be barbaric and violent tests revealing nothing of truth or lies. These were ancient judicial practices where the accused was subjected to dangerous perils. Death would indicate guilt, and survival suggested innocence. These pre-modern trials were eventually forbidden by ecumenical council of the Roman Catholic Church, and were replaced by the Inquisition (trials and torture to combat heresy). By the Late Middle Ages the practice of trial by ordeal was dying out, but was only finally discontinued in the 16 th century.

Various trials fall under ordeals, such as trial by fire, poison, or snake. The fire ordeal required suspects to walk across coals or red-hot iron, or pull stones from boiling water. In ancient Iran, trial by fire was the ultimate test of an accused, and survivors were said to be protected by the judicial divinity Mithra.

Fire ordeal

Fire ordeal. The trial of Sita in the Ramayana (Nirmukta)

Trials by water are often associated with witch-hunts of the 16 th and 17 th centuries in America, but they had been practiced for thousands of years. The unfortunate accused would be submerged in water, and the outcome was almost always fatal. It was assumed a crime would weigh upon the accused, drowning them, and if they were innocent they would survive. However, in later witch hunts those who sank were considered innocent, while floating indicated guilt, lies, and witchcraft. The accused was dead either way.

Witch Hunt

Witch Hunt. The cucking/ducking stool (ListVerse)

Modern Lie-Detection

Our modern judicial systems rely on forensics, the scientific method, and psychological and physiological evidence, sometimes compiled using a polygraph, commonly known as a lie detector. The lie detector is three devices – one to record respiration, one to read blood pressure, and one to determine electrical responses of your skin. Combined, this test is intended to measure changes in physiological arousal, or stress.

But this modern lie-detection technology is largely an advanced psychology test, suggest experts. The horrible truth about the lie detectors is that they’re unreliable at discerning fact from fiction, or truth from lies. Though they’re a somewhat comforting cultural icon, they’re considered by scientists and psychologists to be unreliable, and invalid means of lie detection.  Their findings are largely inadmissible in western courts.

Lie Detector

American inventor Leonarde Keeler (1903-1949) testing his lie-detector. (Public Domain)

In fact, HuffingtonPost writes that there’s not a behaviour that always signals if someone is lying or telling the truth. Deception expert Maria Hartwig, Ph.D., an associate professor at the John Jay College of Criminal Justice told HuffingtonPost, “just by looking at a person's behavior and listening to their statements, you will obtain an accuracy rate of about 54 percent, which is just slightly above the rate that you would obtain if you were just guessing. […]The classic idea that people, in general, believe -- and that … many of these so-called experts propagate -- is that liars give themselves away by gaze aversion, not looking you in the eyes; that they fidget, they change their posture, they pick on their clothes […] All those ideas turn out to be false”.

An abstract for an article from the American Psychological Association notes that modern lie detectors  are “basically a psychological test, although with questionable psychometric merit, that assumes that liars are aware of their lying, which in turn causes measurable emotional reactions. This simplistic assumption was not always shared by the ancients, but it now has widespread contemporary acceptance. The polygraphic technique based on this assumption yields unacceptably high error rates that have had ruinous effects on the lives of many misclassified truthful persons.”

In future, as our understanding of the human brain advances, we may be able to see into the very minds of people and judge if they’re lying or not. But with guesswork and questionable lie-detector machines as our tools right now, have we come that much farther from dry rice and sooty donkeys? The more we learn of science, technology, neurology and psychology, the closer we are to realizing we still cannot tell truth from lies, or guilt from innocence, with much greater accuracy than the ancients did.

Featured image: La Bocca della Verità  - the Mouth of Truth (Wikimedia Commons)


The Roman Trickery of Bocca della Verità - RetroBlogRome

Forensics in Antiquity – Wikipedia

The Truth About Lie Detectors (aka Polygraph Tests) - APA

How To Tell If Someone Is Lying To You - HuffPost

Trial by Ordeal - Wikipedia

The Lie Detector: Does it Really Work? - LineonLife

By Liz Leafloor



The conventional explanation for the Catherine Wheel (trial by ordeal contraption) makes no sense.  The more logical explanation is that the body of the accused was strongly spun clockwise.  A good person or truth teller would be able tolerate the clockwise spinning, but a bad person or liar would not be able to.  In contrast, were the contraption to fall into the hands of a bad person, anti-clockwise spinning could be used as torture device.    

As relates, consider the likely conversations among the various purveyors as to which way the carnival rides should spin.  Interesting history there!

I think they should use some of these on the Jeremy Kyle show make the lie detecxtor results more interesting :)

DeAegean's picture

I twitch a lot and used to have trouble looking people directly in the eye regardless of lying. Modern tests in a dark room with an interrogator would defiintely have me setting off the machine.

The dry mouth makes sense because sometimes when I am around people I don't like talking to my mouth will become very dry and also bitter.

rbflooringinstall's picture

The only one of those ancient lie detection methods that makes any sense at all is the Chinese rice thing.

Peace and Love,



Liz Leafloor is former Art Director for Ancient Origins Magazine. She has a background as an Editor, Writer, and Graphic Designer. Having worked in news and online media for years, Liz covers exciting and interesting topics like ancient myth, history,... Read More

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