By conquering the current called Udāna the Yogi does not sink in water or in swamps, he can walk on thorns etc., and can die at will.
In plain words: By mastering Udana, the energy that moves through the chest and upper body, the yogi becomes light. He does not sink in water or mud. He can walk on thorns, and he can choose when to die.
Udana is the name of the nerve current that governs the lungs and all the upper parts of the body, and when he is master of it, he becomes light in weight. He does not sink in water; he can walk on thorns and sword blades, and stand in fire, and can depart this life whenever he likes.
Namaste.
A calm guide to life, the mind and the old teachings.