While certain people might seem like they're better at lying than others, it turns out that anyone can train themselves to fib. Researchers at Northwestern University found that 20 minutes of practicing makes telling lies as easy as telling the truth.

In a small study of 32 people, researchers asked half of the participants to remember three facts about a false identity: a new name, date of birth, and hometown. Researchers then asked volunteers to answer the question "Is this true of you?" for different facts and to press a "yes" or "no" button in response. The people with a false identity were asked to practice lying by selecting "yes" for the new facts. Researchers measured response time and accuracy and, after 270 trials, or 20 minutes of practice, the liars' values matched those of the truth-tellers.

Why does it take training to become skilled at telling a lie? Because lying requires some mental juggling, says Xiaoqing Hu, a study co-author and psychology doctoral candidate at Northwestern University. When you tell a lie, you have to hold two conflicting answers in mind and suppress the one that's true. However, 20 minutes is enough time to memorize the lie completely, which means no extra thought is needed to tell it. Plus, psychologically, it's possible that after repeating something to yourself over and over again, you can subconsciously convince yourself that it's true, even when you (logically) know it isn't.

"The way our minds work can be quite flexible," Hu says. "We can be very good at 'deceiving' ourselves to be better. For instance, if I told myself repeatedly 'I am competent, I am smart, I am good at math,' then such self-initiated 'training' might also help one's real performance," he says. "This could be similar to the self-fulfilling prophecy, but with training." (Could you use a pep talk? Here are even more ways to Boost Your Self-Confidence.)

Unfortunately, not all lies are so positive. In the absence of a polygraph test or hard evidence, here are three ways to tell if someone is lying to you--and a few "tells" that just aren't effective.

Someone might be lying to you if...

It takes them too long to respond
If someone takes a long time to respond to a simple question, then you should find it suspicious. But there's no cutoff for too long--it's relative. In his research, Hu compares response times between two types of questions of similar complexity: ones that he knows people will respond to truthfully and ones that they might respond to deceptively. If replies to the second type of question take much longer than the first, then the answers could be lies. So if you ask someone to tell you their favorite color and the year they were born, their response times should be about the same.