The male frog makes the croaking sound by filling his air sac with air and releasing it. We got to practice this by blowing balloons and slowly letting out the air. We also discovered that we have voice boxes with which we can communicate and make noise. It works in a similar way: when the air passes through, it causes vibrations in the voice box, and this is the noise that we hear. When air passes through in different ways, different sounds are made. This is just like the balloon (or air sac)= when we tried pulling on it to make the whole smaller, it made different sounds.