In many cases, a pathological liar actually believes what they are saying is true. This is a sever mental disorder which requires in-depth therapy. In that case, I believe it is possible for the lie to go undetected. Still, there are differences in opinion as to whether a pathological liar actually knows that what they are saying is indeed a lie. In other words, some would say the pathological liar knows that what they are saying is a lie, but can not help themselves and therefore state the lie. In this case, I believe the lie would be detected.
Answer
Yes some people can beat the lie detector test because it's not 100% accurate. As the above poster said a pathological liar may beat it, and also a well-trained person who controls their mind and heart rate can also beat it. There is experimentation's in the Army where soldiers are trained to beat any method of obtaining information. The brain is a wonderful thing.
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