Here's a great animated video that helps explain away a myth about public speaking that convolutes some science: The Mehrabian theory about the importance (or lack thereof) of words in communicating a message. Lots of coaches cite this theory to suggest that it's your appearance or visual skills that matter far more than the actual content of your presentation. The video's an amusing lesson in clarification (the theory wasn't designed to cover all speech, or even presentations--just situations where someone is expressing feelings and when their words don't match their facial expressions).
This isn't to say that the visual doesn't count. It does. But your word choices matter, too--perhaps more than you've been told. Enjoy the video!