Popcorn stitches, like puff stitches, "pop" out on the right side of the fabric, but instead of being flat on the wrong side, the stitches are pressed in toward the right side.
Popcorn stitches are worked as follows:
1. In the indicated stitch, work 5 dc as though you were making a shell. You should have one loop left on the hook afterward.
2. Carefully remove the loop from the hook, insert the hook into the first dc of the shell, and then replace the loop onto the hook.
3. Draw the loop through the first dc, allowing the remaining dc to "pop" out toward the front. Your popcorn is now complete.