The vital force of a living entity includes the five kinds of air working within the body, which are known as prāṇa, apāna, vyāna, samāna and udāna. The vital force is compared to a serpent because a serpent can live by simply drinking air. The vital force carried by the air is described as the pratīhāra, or the bodyguard. Without the vital force one cannot live for a moment. Indeed, all the senses are working under the protection of the vital force.