People tell fibs. Some are harmless. Teachers burdened by a pile of marking often tell pupils that they are really pleased with last week's work and have decided to let them off homework. Some are devious. The air of innocence adopted by classroom villains faced with their misdemeanours has to be seen to be believed.
Some liars are downright dangerous, like the colleague who attempts to spin a web of deceit to cover incompetence, or the interviewee whose application form is a tissue of lies, possibly hiding a murky past. Unfortunately, as last week's TES revealed, police checks on all would-be teachers' criminal convictions are at least two years away.
Experts in body language claim that spotting a liar can be relatively easy. Dishonest behaviour is often shown by a combination of key phrases and gestures, say the books. "People who exhibit a sudden increase in nervous hand-to-face contact, such as nose scratching or sitting back in their chair to distance themselves from the questioner, are probably lying," says one such guide. Other tell-tale give-always are supposed to include verbal fillers such as "sort of" and "you know" and the avoidance of eye contact.
But recent research indicates that lying may have roots deep in our evolutionary past and that spotting a liar can be nigh on impossible. Paul Seager, a psychologist at the University of Hertfordshire, filmed 10 actors talking about their favourite films. Half were lying. Volunteers were asked to spot the five who were making it all up and scored little better than they would have done by flipping a coin. Just 55 per cent of the guesses were right.
The argument that liars are easy to spot relies on theories that argue that deception requires sophistication; it is learned behaviour. Small children, the theories suggest, do not have the capacity to deceive successfully. Yet research at the University of Portsmouth appears to show that three-year-olds can spin a yarn as successfully as any adult.
Paul Newton and Vasudevi Reddy asked mothers to analyse the day-to-day behaviour of their young offspring. Deceptions included feigning indifference to a toy so that another child might consider the object not worth having, as well as the well known ploys of crying for attention and pretending to be asleep.
In Scotland, two other researchers, Andrew Whiten and Richard Byrne collected examples of deception among monkeys and apes. One monkey being pursued by others after some misdemeanour looked up and emitted an alarm call which would normally signal the approach of a predator. His pursuers abandoned the chase and climbed to safety, but there was no predator.
Whiten argues that deception has played an important part in the evolution of primates. When the first hominids left the forests to walk upright they were ill-equipped to take on the predators that prowled the plains. Our ancestors survived by using the rudiments of intelligence to outwit their rivals. So the child who calmly explains that he has no knowledge of where Tracy's rubber has disappeared to could be utilising the benefits of half a million years of evolution.
But there is hope for the hard-pressed teacher or manager faced with a raft of reasons why Darren hasn't done his homework or why Miss Frost is absent every Monday morning. Paul Seager's research in Hertfordshire shows that our ability to detect liars improves once we have seen a speaker behaving truthfully.
"We found that people were then getting it 65 per cent right in spotting liars," he told a psychology conference last year. If we have evolved as mendacious manipulators it follows that we would need the capacity to detect deceit in others.
"For a job applicant, recruiters should lay on an informal lunch and circulate between the candidates asking questions about their journey," advised Mr Seager. Observation of honest interaction will help spot any attempts at dishonesty in the interview.
For 3C, the situation is more complicated. Teachers are often faced not with one fibber, but a whole group supporting each other's imaginative porkies. The temptation to double-bluff the kids and threaten some heinous punishment unless they come clean is ill-advised. Schools are a trifle short on heinous punishments and the kids know it.
Paul Seager's observation theory suggests that teachers are most likely to discover the truth by talking to the children they know best - though when it comes to deception adolescents are at the top of the evolutionary tree.
"After all," says Byron, "what is a lie? Tis but the truth in masquerade."
Machiavellian Intelligence, edited by A Whiten and R Byrne, OUP