(Mother Yasoda looks in Krishna's mouth—click to enlarge)
Another day, when Kṛṣṇa and Balarāma were playing with Their friends, all the boys joined Balarāma and told mother Yaśodā that Kṛṣṇa had eaten clay. On hearing this, mother Yaśodā caught hold of Kṛṣṇa's hand and said, "My dear Kṛṣṇa, why have You eaten earth in a solitary place? Just see, all Your friends including Balarāma are complaining about You." Being afraid of His mother, Kṛṣṇa replied, "My dear mother, all these boys, including My elder brother Balarāma, are speaking lies against Me. I have never eaten clay. My elder brother Balarāma, while playing with Me today, became angry, and therefore He has joined with the other boys to complain against Me. They have all combined together to complain so you will be angry and chastise Me. If you think they are truthful, then you can look within My mouth to see whether I have taken clay or not." His mother replied, "All right, if You have actually not taken any clay, then just open Your mouth. I shall see."
When the Supreme Personality of Godhead Kṛṣṇa was so ordered by His mother, He immediately opened His mouth just like an ordinary boy. Then mother Yaśodā saw within that mouth the complete opulence of creation. She saw the entire outer space in all directions, mountains, islands, oceans, seas, planets, air, fire, moon and stars. Along with the moon and the stars she also saw the entire elements, water, sky, the extensive ethereal existence along with the total ego and the products of the senses and the controller of the senses, all the demigods, the objects of the senses like sound, smell, etc., and the three qualities of material nature. She also could perceive that within His mouth were all living entities, eternal time, material nature, spiritual nature, activity, consciousness and different forms of the whole creation. Yaśodā could find within the mouth of her child everything necessary for cosmic manifestation. She also saw, within His mouth, herself taking Kṛṣṇa on her lap and having Him sucking her breast. Upon seeing all this, she became struck with awe and began to wonder whether she were dreaming or actually seeing something extraordinary. She concluded that she was either dreaming or seeing the play of the illusory energy of the Supreme Personality of Godhead. She thought that she had become mad, mentally deranged, to see all those wonderful things. Then she thought, "It may be cosmic mystic power attained by my child, and therefore I am perplexed by such visions within His mouth. Let me offer my respectful obeisances unto the Supreme Personality of Godhead under whose energy bodily self and bodily possessions are conceived." She then said, "Let me offer my respectful obeisances unto Him, under whose illusory energy I am thinking that Nanda Mahārāja is my husband and Kṛṣṇa is my son, that all the properties of Nanda Mahārāja belong to me and that all the cowherd men and women are my subjects. All this misconception is due to the illusory energy of the Supreme Lord. So let me pray to Him that He may protect me always."
(Kṛṣṇa Book, Chapter 8, "Vision of the Universal Form.")