SB 4.25.35

ete sakhāyaḥ sakhyo me
 narā nāryaś ca mānada
suptāyāṁ mayi jāgarti
 nāgo ’yaṁ pālayan purīm
Synonyms: 
ete — all these; sakhāyaḥ — male friends; sakhyaḥ — female associates; me — my; narāḥ — men; nāryaḥ — women; ca — and; māna-da — O very respectful one; suptāyām — while sleeping; mayi — I am; jāgarti — keeps awake; nāgaḥ — snake; ayam — this; pālayan — protecting; purīm — this city.
Translation: 
My dear gentleman, all these men and women with me are known as my friends, and the snake, who always remains awake, protects this city even during my sleeping hours. So much I know. I do not know anything beyond this.
Purport: 

Purañjana inquired from the woman about those eleven men and their wives and the snake. The woman gave a brief description of them. She was obviously without full knowledge of her surrounding men and women and the snake. As stated before, the snake is the vital force of the living being. This vital force always remains awake even when the body and the senses become fatigued and do no work. Even in the state of unconsciousness, when we sleep, the snake, or the life force, remains intact and awake. Consequently we dream when we sleep. When the living entity gives up this material body, the vital force still remains intact and is carried to another material body. That is called transmigration, or change of the body, and we have come to know this process as death. Actually, there is no death. The vital force always exists with the soul, and when the soul is awakened from so-called sleep, he can see his eleven friends, or the active senses and the mind with their various desires (wives). The vital life force remains. Even during our sleeping hours we can understand by virtue of our breathing process that the snake lives by eating the air that passes within this body. Air is exhibited in the form of breathing, and as long as breath is there, one can understand that a sleeping man is alive. Even when the gross body is asleep the vital force remains active and alive to protect the body. Thus the snake is described as living and eating air to keep the body fit for life.