Srimad-Bhagavatam: Canto 3 - Chapter 1 - Verse 21

Sanskrit:

तिरश्चामष्टम: सर्ग: सोऽष्टाविंशद्विधो मत: ।अविदो भूरितमसो घ्राणज्ञा ह्यद्यवेदिन: ॥ २१ ॥

ITRANS:

tiraścām aṣṭamaḥ sargaḥso ’ṣṭāviṁśad-vidho mataḥavido bhūri-tamasoghrāṇa-jñā hṛdy avedinaḥ

Translation:

The eighth creation is that of the lower species of life, and they are of different varieties, numbering twenty-eight. They are all extensively foolish and ignorant. They know their desirables by smell, but are unable to remember anything within the heart.

Purport:

In the Vedas the symptoms of the lower animals are described as follows: athetareṣāṁ paśūnāḥ aśanāpipāse evābhivijñānaṁ na vijñātaṁ vadanti na vijñātaṁ paśyanti na viduḥ śvastanaṁ na lokālokāv iti; yad vā, bhūri-tamaso bahu-ruṣaḥ ghrāṇenaiva jānanti hṛdyaṁ prati svapriyaṁ vastv eva vindanti bhojana-śayanādy-arthaṁ gṛhṇanti. “Lower animals have knowledge only of their hunger and thirst. They have no acquired knowledge, no vision. Their behavior exhibits no dependence on formalities. Extensively ignorant, they can know their desirables only by smell, and by such intelligence only can they understand what is favorable and unfavorable. Their knowledge is concerned only with eating and sleeping.” Therefore, even the most ferocious lower animals, such as tigers, can be tamed simply by regularly supplying meals and accommodations for sleeping. Only snakes cannot be tamed by such an arrangement.