Lie detector is a modern instrument that detects the liars. It uses the changes in the body to say whether one is telling the truth or not. In Ancient India they used different techniques to find the truth. Chandogya Upanishad has the earliest reference to one test called a Hot Axe Test. This test was given to people charged with thefts in Ancient India. It followed the same principles that are used in the modern Lie Detectors.

An axe would be made red hot and the accused person would be asked to hold it in his hand. If the hand was not burnt, he would be acquitted. It shows that he was innocent. If his hand was burnt he would be convicted and severe punishments would follow the convictions. During the days of Guptas there were severe punishments for thefts and robberies. Because of severe punishments and great prosperity there was no theft and people slept without locking their doors, says the Chinese traveller Fa Hien (337-422 AD).

Adi Shankara, the great philosopher, also alluded to this hot axe test in his Viveka Chudamani (sloka 332).The reference in the Chandogya Upanishad appears thus:
VI-xvi-1: ‘Dear boy, (The officers of the king) bring a man, holding him by the hand (while saying) “He has taken something, he has committed a theft, heat the axe for him”. If he is doer of that, then he makes himself false. And being addicted to falsehood, he covers himself with falsehood and grasps the heated axe; he is burnt, and then he is punished.

VI-xvi-2: ‘If, however, he is not the doer of that, then he makes himself true. And being attached to truth, he covers himself with truth and grasps the heated axe; he is not burnt and then he is released.
VI-xvi-3: ‘And as in this case he (the man attached to truth) is not burnt, (similarly a man of knowledge is not born again). Thus has all this world That for its self. That is the true. That is the Atman. That thou art, O Svetaketu.’ From his words Svetaketu understood That – yea, he understood.

Snake Pot Test

Kulasekhara Alwar is one of the twelve Vaishnavite saints of Tamil country. He ruled Chera country (modern Kerala) around 800 AD. He was a great devotee of Vishnu and devoted much of his time in listening to Ramayana, Maha Bharata and Bhagavatha. Some of his court officials did not like this. They wanted to create a rift between the priests and the king. So they falsely accused the priests of stealing the temple jewels. The king did not believe this story and knew the motive of the accusers. In those days if someone tells a lie he would be asked to put his hand in a pot full of hungry cobras. If one has done anything wrong they would definitely avoid instant death by the snake bites. The king proposed that he would put his hand in the pot of snakes and if he has come out unscathed then the story of theft is false. He did this and came out unharmed. He did it on behalf of the priests
Story of Mandana Mishra

Adi Shankara was victorious in his debates and defeated Gurus of various sects in Hinduism and Buddhism. He had to meet a giant in Mimamsa philosophy. When they wanted to discuss Advaita philosophy they wanted a judge to say who has won the discussion. In those days people were so honest that once they are defeated they would accept the defeat and embrace the philosophy of the opponent who won the debate. There was none to judge their debate except Mandanamisra’s wife Sarawani. Since both of them were intellectual giants they accepted Mandan’s wife as judge. She was equally a great scholar. But she was very much embarrassed and told them that she being the wife of one of the debaters wouldn’t be a proper person to be the judge in this contest. So she proposed a very good idea. She asked both Mandana and Shankara to wear flower garlands and told them the wearer of the garland that withers first was the loser.

The argument went for weeks and at last Mandana’s garland withered first. Then Shankara had to debate with his wife. When she was also defeated by Shankara both husband and wife became disciples of Adi Shankara. Mandana became Sureshwaracharya in his later life.
Sita’s Agni Pareeksha (Fire Test)
When Rama’s wife Sita Devi was suspected by a washer man of the city Ayodhya Rama asked Sita to undergo Fire Test to prove her purity and integrity. She jumped in to a fire pit and came unscathed. Even today the Fire Walking ceremony is done in several South Indian villages. It is an ancient custom to prove one’s innocence and integrity.

Tamil Lie Detector

Ancient Tamils followed a different test 2000 years ago. One of the Sangam Tamil Books Kalitokai describes this strange test. If a liar stands under a tree the tree would wither away. If he is not a liar the tree would be ever green. Palai Padiya Perum Katunko (Palai Kali 33) sang about this test. A woman who suffers from separation lamented that her condition was like a tree that was made to wither by a liar.

Science behind Lie Detectors

There is a scientific explanation for all the above tests. It is the same principle that the modern Lie Detecting instruments follow. A Polygraph, popularly known as Lie Detector, records graphically certain body activities such as respiration, blood pressure, pulse rate and changes in the electrical resistance in the skin. Marked changes in these activities when a person answers a question may indicate that the person is lying. Facial expressions and linguistic changes are also taken into account.

If we look at the case of Tamil tree or Mandana’s garland we can see why they wither away. The temperature changes in the body make them wither away. Whoever is agitated and doesn’t see the reason or truth feels hot. More over the fear makes one to produce more adrenaline. Animals like dogs and snakes can easily sense it. They have powerful smell organs. If one is not agitated and focussed, calm and quiet that person wouldn’t be harmed even by an agitated animal. When a person has full concentration on a certain thing (truth or God) neither extreme heat nor cold would affect that person. Yoga practitioners knew this very well. So we can see science behind the above anecdotes.