It is amazing to many how much information is communicated though body language during an ordinary conversation. The importance of your non-verbal communication is amplified in a public speaking setting. If you have never given much thought to what your body is saying while you speak, try this little experiment.
- Stand (don't sit) in front of your iPhone/Android set far enough away to view your whole body.
- Video yourself talking about a controversial topic (e.g. your views on gay marriage) for 1 minute.
- Share the video with someone else, but mute the volume.
- Ask them what they think you were saying.
As long as they are not experts in lip reading, they are very likely to interpret your communication very differently than you do. The vast majority of the emotional content in your message is communicated though non-verbals like body language, posture, and vocal tone.
Improv Comedy Troupes, like The Laff Staff in Jackson Hole, WY, play a fun game during performances that emphasizes how much information is communicated non-verbally. The game is called Deaf Replay, and it involves three pairs of actors. The first pair is instructed to make up a scene based on a suggestion from the audience. The remaining two pairs are kept off stage with headphones blaring loud music so that they cannot hear the audio portion of the scene. The first group must then try to reenact the scene from the first pair of actors, using all of the same body movements, and trying their best to guess what the dialogue was between the first to actors. The third group, who were only allowed to watch the 2nd group of actors perform (again, no audio), try to reenact the scene from the 2nd pair. It never fails that the three scenes are COMPLETELY different, and hilarious.
If you have never scene improvisational theater performed, I highly recommend it, as it will help you understand some of the major fundamentals of communicating effectively in any situation.