脫胎換骨 A Change of Bone and Womb
這裡卻暗暗念動真言，誦動咒語，將仙氣吹入他三人心腹之中，把元神收歸本舍。傳與口訣，各授得萬千之膂力，運添了火候，卻像個脫胎換骨之法。这里却暗暗念动真言，诵动咒语，将仙气吹入他三人心腹之中，把元神收归本舍。传与口诀，各授得万千之膂力，运添了火候，却像个脱胎换骨之法。
逐句解 Line by line
Here he quietly set the true words going and intoned the spells, blew immortal breath into the hearts and bellies of the three of them, and gathered their primal spirits home to their own dwelling.
真言 is the Chinese for mantra, the true word; 咒語 is the spoken spell. 仙氣, immortal breath, is blown in — 氣 being the vital energy that inner alchemy works on. 元神 is the primal spirit, the part of a person that wanders in sleep and in death, and 舍 is shè here, a dwelling: he is putting each boy's spirit back in its house.
He handed on the spoken formula, granting each of them the strength of ten thousand, worked in the added degree of fire, and it was very like a method for changing the bones and casting off the womb.
膂力 is spinal strength, the power along the backbone — the exact word for brute physical force. 火候, the fire's timing, is the central technical term of Chinese alchemy: the precise regulation of heat that makes the elixir work, and used since for the mastery of any craft. 脫胎換骨, shedding the womb and exchanging the bones, is the alchemical phrase for total transformation, and it is still ordinary Chinese for being completely made over.
The transmission is a piece of internal alchemy, described in its proper technical vocabulary and performed in about fifty characters.
The phrase for the fire's timing is worth keeping. It is the alchemist's term for knowing exactly how hot and how long, and it became the standard Chinese word for the judgement that separates a master of anything from a competent practitioner.
What is being given is not skill. Pilgrim said the boys were not strong enough and could not be taught, and his answer was to change what they are made of.