Most people rarely lie and therefore operate with a "truth bias," assuming others are also being truthful. This cognitive default, while efficient for most interactions, becomes a major vulnerability that people with dark personality traits exploit. They can lie frequently because it rarely occurs to others to question them.

There is no single giveaway for lying that applies to everyone. The key is to first understand an individual's normal pattern of speech and behavior (their baseline). Deception is revealed through deviations from this norm, such as adding excessive, unnecessary details to a story to bolster its credibility.

Priests manipulating trials by fire was a feature, not a bug. A defendant's willingness to undergo the ordeal signaled their innocence to the priest. The priest, acting as 'God's instrument,' would then rig the test to ensure an acquittal, reinforcing the system's perceived divine legitimacy.

Asking, "Is there any reason [evidence] of you might exist?" creates a powerful dilemma for a guilty person. They must either lie and risk being proven a liar, or place themselves at the scene of the crime. An innocent person, by contrast, will answer quickly and without hesitation.

We consistently overestimate our ability to detect lies by reading body language. Empirical research shows our accuracy is only slightly better than a coin flip (around 54%), yet the belief in this skill persists as a strong cognitive bias.

According to "Truth Default Theory," telling the truth is our natural, low-effort state. Lying is cognitively demanding as it requires inventing and tracking a false narrative, which violates the human tendency toward cognitive ease.

Ordeals were not barbaric tests but a clever sorting mechanism. Guilty defendants, believing God would ensure they were burned, would confess beforehand. Innocent defendants, believing God would protect them, willingly underwent the (often rigged) test, thus revealing their private information.

The technique for creating a 'deception probe' exists, but it's nearly impossible to implement because we can't reliably collect training data. Deception is about intent and a model's internal 'state of mind,' which is difficult to label. A pragmatic alternative is to build probes for simpler concepts like 'true' vs. 'false.'

When people are nervous or lying, their blink rate often increases dramatically. This is an unconscious 'eye blocking' behavior where the brain tries to shut out external stimuli to process the cognitive load of deception. It's a danger zone cue that manipulators cannot easily control.