True Men of Old Breathed From Their Heels
Zhuangzi uses the physical depth of a person's breathing as evidence for how thoroughly their fear and self-division have actually settled.
Zhuangzi's portrait of the zhenren, the "True" or "Realized" Man, lists behavior before doctrine: unafraid of danger, without regret over what's lost, not elated by success, able to climb high without trembling, enter water without getting wet, enter fire without being burned — descriptions of someone whose grip on reality has stopped depending on ordinary fear. The detail that follows directly is physical: the True Man's breath comes from his heels, the ordinary person's breath comes from his throat, a claim, whether meant literally or as metaphor for depth of composure, that ordinary anxiety shows up as shallow, throat-level breath, while the True Man's reaches all the way down. Zhuangzi adds that people bent under argument and desire speak as though they were retching, their words catching in the throat the same way their breath does. The passage, from chapter 6, ties physiological description directly to spiritual attainment, treating breath, not belief, as the observable evidence of how deeply a person's realization actually runs.
The true man breathes from his heels; ordinary people breathe from their throats.
Zhuangzi