Nauli is the foremost of Hatha Yoga practices. It kindles the digestive fire, removing indigestion, sluggish digestion, and all disorders of the doshas, and brings about happiness.
Hatha Yoga Pradipika II:34

Uddiyana Bandha is so-called by the yogis because through its practice the prana (is concentrated at one point and) rises through the central channel. The Bandha described is called the rising or flying Bandha, because through its practice, the great bird (Shakti) flies upward with ease.
Hatha Yoga Pradipika III.55-6

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