Slinky spring provide us clue about how sound travels through the medium. One can see compression and rarefaction in the slinky spring while the wave is passing through it. 
Ask students to watch the video of slinky spring.

Video 4.2 (a) shows a single wave pulse traveling in slow motion in a golden coloured slinky spring. 
Video 4.2 (b) shows consecutive waves travelling so many times, one can also see reflection of the wave.

You can demonstrate or ask students to do it, if slinky spring is available.