Find the Liar by Increasing His Cognitive Load With Open-Ended Questions
Lying on the spot is hard to come up with even for experienced liars. If you suspect someone is feeding you a fake story, highlight it by making you think too much about your story.
As the blog Barking Up the Wrong Tree explains, the liar naturally wants the lie to be simple. The fewer details they have to come up with on the spot that all agree with each other, the easier it will be to be convincing. However, you can counter this by asking open-ended questions that increase the cognitive load on the person you suspect is lying. The more you make them think, the less likely they are to tell a true story:
So if you want to get the liar to reveal himself, you want to increase their cognitive load. The more they think, the more likely they are to make a mistake.
How to do it? Police detectives ask open-ended questions that make them keep talking. Unexpected questions that they are not ready for are the best. Anything that tires someone mentally is good.
The more you can get them to talk, the more likely they are to get confused. Open-ended questions are best for keeping them in conversation (as opposed to simple yes or no questions) because they force the person to come up with the details themselves. The more detail you have, the easier it is to find inconsistencies.
How to tell if someone is lying: 5 Research Backed Secrets | Bark on the wrong tree