There's a sure-fire way to cheat on lie detector tests. And anyone can do it.

When was the last time you needed to cheat a polygraph test?

Yesterday? Last year? Never?

According to certified polygraph expert, you shouldn’t have to worry about cheating a polygraph test anymore. Because that’s what he is here for.

In the latest episode of This American Life, Doug Williams shares how he learnt, over the years, to beat the test.

After joining the police force in Oklahoma in his 20s, but 1972 and after going to polygraph school in New York, he was a certified expert in lie detector tests. All day every day, he run polygraph tests.

Before long, he grew tired. He began to doubt their effectiveness, he knew how to intimidate people to get them right. He believed the "more heinous the crime", the more "likely an innocent will fail". After all, even the accusation of a serious crime is bound to induce the sweats and get your pulse up.

"I began to doubts in the tests after a while, I knew I could control my breathing but I didn't know for sure how to control the cardio and the blood pressure," he told the radio show. "It wasn't until my friend came in and started talking about the pucker factor and tightening up the anal sphincter muscle when he was under stress."

Yep, that's right. All you need to do is, erm, clench your anus in order to beat a lie detector test.

"After he left, I just hooked myself up to the polygraph test... and tightened up my anal sphincter muscle like I was trying to stop my bowel movements and low and behold there was the most gigantic, wonderful, naturally occurring cardio rise, accompanying a GSR rise."

(A GSR, of course, being galvanic skin response, which is basically the increase or decrease of sweat activity in your hands.)

Williams adds that you "can cause a reaction at will...you [just] have to pick the right time to do it".

Of course, in 2015, he plead guilty to obstruction of justice and mail fraud for teaching people how to pass lie detector tests after offering for those needing to sit one, so perhaps sharing the advice so publicly wasn't so clever after all?

And in his own words: "It takes an a-hole with a little training to beat an a-hole with a little training."

Thankfully, according to Victoria Police, the Homicide Squad do utilise polygraph testing as part of investigations but these tests are "only used as an indicator" in a host of other methods and "are not admissable as evidence in court".

Phew.