A professor once said, "Words conceal rather than reveal". If that's true, how does the listener hear the real message? The answer is the study of pragmatics. Non-verbal communication is as important to every public speaker as the words they prepare. But too often, public speaking becomes an exercise in memorizing words without much thought to their physical presentation.
If the public speaker is unprepared, it will be communicated through nervous body language. The body will betray the presenter every time. Most of the message is non-verbal. For that reason, it's imperative that public speakers study pragmatics. Watch this video to learn about body language.