Fire, verily, is Udāna. Therefore, when fire is extinguished, one goes to re-birth, with the senses united to the mind.

Udāna — the ascending breath — is identified with Tejas (fire, light). It is the force that rises, that ascends, that goes upward.

When a person dies, upāśānte-tejāḥ — when the fire (the light, the heat) is extinguished — the udāna carries the being toward punar-bhava (re-birth). The indriya (senses) and manas (mind) remain united (sampadyamānaiḥ), constituting the karmic package that determines the next existence.

This is a description of the process of death and transmigration. The udāna is the vehicle that transports consciousness from one body to another. In yoga practice, especially in certain advanced techniques, the yogī learns to control udāna in order to be able to leave the body consciously at the moment of death (videha-mukti).

Fire always ascends; thus udāna always rises. The yogī cultivates this ascending fire through spiritual practice.