It's harmless, but don't knock hard at first, it will hurt, and it should be done step by step. Try slapping several times to find out the strength that your body can bear now, and then stick to slapping 1000 times on the basis of this strength. This 1000 is actually a warm-up period, which is used to get your body used to hitting with a small hammer. After these 1000 tricks, we will enter the formal practice step: 1, find a flat place to lie down, and if we practice, it is best to lie on the bed. 2. Put a book 1cm thick on your chest. 3. Relax and take a deep breath. Take a small hammer in your right hand and knock hard on the book on your chest. The hitting force can be about twice as strong as your previous warm-up stage. ",shout at top of voice while knocking. . . "。 5. Knock 1000 times repeatedly every day. Knock harder every two days. Replace the small hammer with a bigger one every other month. 6. Stick to this method, and you can break the stone in your chest in less than half a year.