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Two people want to sell you something. One of them is lying.
The first tells you calmly, "I promise you're going to love this."
The second is much more animated. He exclaims: "You're going to [bleeping] love this. It's [bleeping] amazing, totally unbelievable, [bleeping] going to blow you away. Everybody loves it. You're going to love it, too."
How did the researchers come to this conclusion? They saw what happened when they brought in 104 people to play something called "the ultimatum game."
The rules are simple: One person is given a secret sum of money. He's introduced to a second person, and he has to propose to split what he has been given with that second person. The second player, who has no way of knowing for sure how much the first person has been given, can either accept the division as proposed or reject it. If the receiving player rejects the offer, he gets a token sum, but the offering player gets nothing.
Thus, the person with the money has incentives to make his offer seem reasonable, and also possibly to bluff. As the report further explained:
[E]ach game included two minutes of videotaped conversation in which the receiver could grill the allocator with questions, prior to deciding whether to accept or reject the offer. This provided ample opportunity for the allocator to tell the truth about the money, lie, or try to avoid the subject altogether.
"We wanted to create a situation where people could choose to lie or not lie, and it would happen naturally," says the study's lead author, Lyn M. Van Swol, a professor at the University of Wisconsin-Madison. Watching how the players interacted, Van Swol and her colleagues at the University of Wisconsin and Harvard concluded that players exhibited three easy "tells" when they were lying.
The first tell was simply that the liars tended to use a lot more words to make their points than the truth-tellers did.
"Just like Pinocchio's nose, the number of words grew along with the lie," says Van Swol. The only caveat here is that people who deceived simply by omitting facts, rather than offering untrue ones, also tended to use fewer words. So don't consider this tell foolproof.
It turns out that people who swear more often tend to lie more often, too. In the study, this was even more pronounced after the receiving player challenged them.
"We think this may be due to the fact that it takes a lot of cognitive energy to lie," Van Swol says. "Using so much of your brain to lie may make it hard to monitor yourself in other areas."
The final major tell was that liars tended to use third-person pronouns more often ("he," "she," and "they"), presumably instead of making offers and justifications in the first person ("me" or "I").
"This is a way of distancing themselves from and avoiding ownership of the lie," Van Swol explains. Liars also used more complex sentence structure.
In case you're wondering about the human-nature part of this experiment, the researchers divulged that 70 percent of the allocators told the truth about how much money they had received.