Usually once we get to know a person, we can tell whether or not they are telling the truth. For some people we can always tell if they are lying, and some people can lie with a straight face and we never know if they are telling the truth. A common thing I have heard is to watch their eyes and see if they are looking up to the left, and if they are that means they're lying. But some people can look you straight in the eye and lie to you.
The text said to listen to how a person words something if we want to see if they are lying.
I found the different lie detector tests very interesting. I think in general they are a bad way to go about testing a person's innocence. As the text said, a person's bodily reactions to the test may be misinterpreted because they are anxious about a crime they didn't commit, and a guilty person could go free. It seems like its a hard way to determine guilt when there could be many other factors associated with your reactions or brain activity (an example of another test). Whether it is the case of an argument with a friend or the case of a criminal, it is usually impossible to know whether or not a person is lying, and so far there are no good ways to tell 100% of the time.