Use your hand to power the hoop in a back-and-forth motion: the hoop will alternate between hitting the center of your palm and the back of your hand.
用你的手来给呼啦圈前后移动的力：呼啦圈会在你的手掌心和手背上交替着力。
2
Instead of trying to figure out your motion patterns, Gentle Alarm takes a statistical approach: near the end of the night, light sleep and deep sleep alternate every 30 minutes or so.