When delivering a speech let's say you are exemplifying support for something. However, you are actively being sarcastic or only presenting the information with little to no effort and interest, you are contradicting yourself by means of body language and attitude. When you present information about a topic showing that you are against this said topic, but you are acting like it is not a big deal, and not that important, then why even bring it up in the first place? This contradicts yourself as well. It takes away the audience's interest and it takes away their want to be there and listen to something that might very well not matter. Be careful when using body language that could be misinterpreted. This will confuse the audience and give them the opportunity to not want to continue listening.
Little interest is a good point Joe. No one wants to listen to a speech when the speaker is disinterested in the topic.