One day many years ago, at a time when his mouth was still small and delicate, as in fact it used to be, the fox was out walking and happened to notice a Huaychao (native Peruvian bird) singing on a hilltop.
Fascinated by the bird's flute-like bill, he said politely, "What a lovely flute, friend Huaychao, and how well you play it! Could you let me try it? I'll give it back in a moment, I promise."
The bird refused. But the fox was so insistent that at last the Huaychao lent him its bill, advising him to sew up his lips except for a tiny opening so that the "flute" would fit just right.
Then the fox began to play. He played on and on without stopping. After a while the Huaychao asked for its bill back, but still the fox kept on. The bird reminded him, "You promised. Besides, I only use it from time to time; you're playing it constantly." But the fox paid no attention and kept right on.
Awakened by the sound of the flute, skunks came out of their burrows and climbed up the hill in a bustling throng. When they saw the fox playing, they began to dance.
At the sight of the dancing skunks, the fox burst out laughing. As he laughed, his lips became unstitched. His mouth tore open and kept on tearing until he was grinning from ear to ear. Before the fox could regain his composure, the Huaychao had picked up its bill and flown away.
To this day the fox has a huge mouth as punishment for breaking his promise.