Vocal Vowels includes plastic models of five different shapes that mimic the shape of the visitor's vocal tract when they make the sounds of 'ee', 'eh', 'oh', 'oo' and 'ah'. A bellows on the exhibit is compressed to produce a flow of air which passes by the reed of a duck call making a quacking sound, just as the air from the lungs causes the vocal cords to vibrate. Like the vocal cords, the reed produces a complex sound made up of many different frequencies. When the reed is placed at the end of one of the plastic models, only some of the frequencies resonate within the model's cavity producing the distinctive sound.