and large vocal cords. Air was passed over the balloon ends/vocal cords when they were "relaxed" (white bars) or when they were "stretched" (black bars). The frequency of the vibrations (number of sound waves per second) were then recorded with a digital instrument tuner ( Hertz = Hz). The data presented are the averages of five tests for each balloon and each condition. The experiments were carried out by two scientists to determine if  "investigator bias" influenced the results.