Brain scanning equipment can tell if you're lying. That's what a team of US scientists have found.
They discovered that people use different parts of their brain when they lie and when they tell the truth, and a brain scan can show this.
In the experiment, six volunteers were asked to shoot a toy gun and then lie and say they didn't do it.
Three others watched the experiment and were asked to tell the truth about what they saw.
More effort to lie
The brains of all nine were scanned with a strong magnet to show what was going on inside their heads.
Researchers found there was more activity in the brains of the liars than in the brains of the truth-tellers. This suggests it takes more effort to lie.
Using such brain scanning equipment is expensive but it could be used when questioning people suspected of committing a serious crime.
At the moment machines called polygraphs are used to detect lies but some people argue it is possible to fool them.