He has identified a feeling among liars he calls "duping delight".

These include arousal (in particular stress), cognitive load, duping delight, and behaviour control.

Call it cheater's high, or duping delight, but psychologists have long known about the thrill of getting away with pulling one off on others.

Some patients may also be a bit sadistic, Dr. Feldman said, and take "duping delight" in tricking others, especially doctors.

Because Silent Talker is based on a multi-factor model including cognitive load, duping delight and behaviour control, its inventors claim that it is robust to countermeasures.

These signals, which differ for each liar and are virtually undetectable in very skilled liars, can indicate the leakage of emotions the liar would rather keep hidden: guilt, despair, anger, fear, distress, embarrassment or "duping delight," the glee some liars feel at deceiving their targets.