As evidence for her belief that she is good at detecting lies, jenny cites three occasions when she caught friends or family members in blatant lies. jenny may actually be good at determining whether other people are telling the truth or not, but the most likely explanation is:

That Jenny uses body language reading to detect when someone is lying.

Explanation:

Body languages involves every movement that the person does, even the slightest move or tick counts as it.  Most people have a singular characteristic movement when they tell a lie.

Some blink, other touch some part of their body constantly like the hands), some others look to a certain point, etc.

Jenny is most likely to use this as a method for detecting other´s peoples lies, which is very effective once you know look very close to the person and its signs.

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