Inside a frog's mouth, located just behind the tongue, is an opening called the glottis, which leads to the frog's trachea. Also called the windpipe, the trachea leads to the frog's lungs. The esophagus is the larger opening located behind the glottis, which leads to the frog's stomach.
According to Biology Corner, the opening to the glottis must remain smaller than the opening of the esophagus to prevent food from traveling through the wrong opening. If food went down through the glottis, the frog may become ill. In humans and other mammals, the glottis and esophagus diverge further down the throat, making it impossible to see the opening of the glottis.