Only the most gifted public speakers develop the capabilities to read their audiences as they speak to them. What does it mean to read your audience? It means being attuned to how the audience members perceive you, whether or not they are enjoying themselves, whether the atmosphere of the room is comfortable for them, and, in general, how they would like your presentation to proceed.
Since audiences consist of more than one person, how can you make a sweeping generalization about what is likely to be a group of highly diverse individuals? Think of the situation often depicted in films in which an assembled group gets out of hand. The group becomes a mob and demonstrates behaviors such as rioting and vigilantism. Singularly, no members of the mob would act the way they do in the group.
An audience is not a mob, but it potentially shares some of the same characteristics. The people in your audience are greatly influenced by those around them. If you tell a joke, and no one laughs, even an individual who finds the joke humorous will refrain from laughing. Likewise, if the people surrounding an individual show a strong response, such as laughter, that person is likely to respond in the same way. In other words,