Burning Mountain Fire is built on three advances and one retreat: the needle is inserted in three stages to three depths, manipulated at each, then withdrawn in a single movement. It is used to produce warmth and to tonify yang.
Penetrating Heaven Cool reverses the pattern: one advance and three retreats, producing a cool sensation and used to clear heat. Both techniques are demanding in practice and require an unhurried hand, and both are described in the literature chiefly through the sensations they are meant to produce. Their value in modern practice is debated, but they remain the clearest examples of how the tradition builds complex procedures from simple ones.