Entrainment is what happens when an independent periodic body — a footstep, a heartbeat, a swinging arm — locks its own frequency onto an external one, such as a musical beat.

This is most of what dancing is, physically: a body voluntarily tuning its many natural periods — stride, swing, sway — to a shared external frequency.

Which means a dancer's movement is not just inspired by music — it can be measured, cycle for cycle, against it.