Tap once, then hold the phone against your chest and stand still. Like Standstill, sound lives in stillness and large movement silences it — but here what remains is split into three voices:
Sway (teal, low wash) — slow postural drift, below ~1 Hz; it also carries the stereo position. Tremor (amber, high shimmer) — fast jitter from muscle and heartbeat, ~2–8 Hz. Rotation (violet, detuned tone) — turning, from the gyroscope; on phones without one it is estimated from tilt, and the readout says which.
The lanes scroll your last half minute — a live picture of motion your eyes cannot see. Try slow breathing, then a heartbeat-focused hold, and watch which lane answers.