A sound is described as periodic. What does that say about the particles of the medium?

1. Some sound waves can be characterised as periodic waves. 2. For those, the atoms making up the matter experience simple harmonic motion. 3. Each atom oscillates about its own rest position rather than travelling onward. 4. The disturbance moves through the medium, but the matter itself stays put. _Source: OpenStax Physics (high school, CC BY 4.0), Ch 14 "Sound", section Properties of Sound Waves_