A study has found that it takes just one look or an image of a pair of eyes to put the fear of God into a person.
The study's effect may help explain why widespread belief in an omnipresent god has evolved, the Sydney Morning Herald reported.
Pierrick Bourrat, a philosophy research student at the University of Sydney, and his colleagues presented more than 90 people with two stories of moral transgressions, keeping money found in a lost wallet, and faking a resume.
Half were given the stories on a piece of paper with eyes on it, and the other half saw an image of a flower.
Those who saw the eyes expressed greater disapproval of the misdemeanours.
Other research has shown a pair of eyes nearly trebled the money people put in an honesty box to pay for their tea or coffee.
One possible explanation is that the eyes unconsciously trigger a basic mental mechanism humans have evolved to be very sensitive to their impression on other people, so they maintain their own reputation.
And one theory of the origin of religion is that the idea of an all-seeing, all-knowing God who punishes bad behaviour has had a role in the development of this high level of social co-operation.
Bourrat said his study did not prove this. But it showed there was a mental process that the religious idea of a judgmental omniscient being could draw upon.