This week, the senior speech class has been studying how sound is produced in the vocal chords. Our book compared the vocal chords to an air-filled balloon which has the neck stretched; the air passing through the neck of the balloon vibrates and produces the funny sound, similar to how sound is produced in our vocal chords. So, I gave each student a balloon, and we made a lot of loud, strange, funny vocal-chord balloon air vibration noises. This was a very practical lesson.