1. Click the starter project link next to this video.
  2. Add a "change whirl effect" block to create the wave effect.
  3. Add a "change whirl effect by -25" to reverse the wave effect.
  4. Place a wait block after each "change effect by" block.
  5. Make the wave keep going with a "forever" block.
  6. Add a "when flag clicked" block to run this code stack when the flag is clicked.