This is a test of commonsense. Complete the next sentence:

How to be more perceptive
Learn about body language.
Ninety percent of human communication is non-verbal. A person's body language can be voluntary or involuntary, and it is both genetic and learned.
It is a strong indicator of how a person feels, but it can vary from one culture to the next. Those discussed in this article are indicators of body language in western cultures.