A calling frog typically inflates his sac or sacs prior to calling or simultaneously with the production of the first call. The sac is inflated with air from the lungs (lung). If another call is forthcoming and the male frog is not in the process of calling, air is still held in the sac. Sound is produced by a controlled rush of air through the larynx and across its vocal cords (vocal cord). The resulting sound vibrations are amplified by the resonating qualities of the vocal sac or sacs. Unlike vocalization processes of many other vertebrates (vertebrate), frogs broadcast sound without expelling air. Air does not exit the mouth; rather, it cycles back and forth between the buccal cavity and lungs.