The moon is easy tonight, so you decide to cut it open. But, the moon wasn't the moon, it was your big, pale, round tummy. You just cut it open, and now you can see your intestines.
All over the world, people are cutting their bellies open, because they think its an easy moon (versus a normal moon, or hard moon, presumably). This is because they have fallen victim to a spell by Mrs. Chou (ちょう).