A melody is defined as a succession of single notes assembled to form a purposeful sequence. What's the purpose? It's to inspire an emotional response in the listener. Whether the emotion is despair, joy, loneliness, love, or anything else, every melody ever written was meant to inspire an emotional reaction.
As a musician your job is to convey the emotion of your melody with expressive playing. The way you do that is to focus emotion into your playing while you're doing it. This means that you don't just play one note after another and congratulate yourself when you make it to the end — you listen to and interpret what the melody conveys to you emotionally, and then you put that feeling back into your playing when you play the melody to pass the emotional content along to the listener. Even a total non-musician can tell the difference between a song played mechanically and one played with feeling.
Coughing can be a problem when you're playing the harmonica. Before a performance it might be useful to coat your throat, like a singer sometimes does, using cough lozenges. This will help to prevent coughing onstage and can also help to reduce the effects of smoke in the venue if there is any.
The melody is the focal point of a song or piece of music. In vocal music the lyrics are sung to the melody line, and in instrumental music the melody is placed prominently above the accompaniment in volume.
Since the songs discussed in this chapter are probably well known to you, they will serve as a good measure of how well you can play at this point. If you can express the melodies well, then you are probably getting enough practice and gaining an understanding of the harmonica and its abilities.