Why don't cast saws hurt the skin under the cast ?

Why don't cast saws hurt the skin under the cast? Well, you might think that the doctor takes extra precautions during this procedure, but the answer actually lies within the saw, you see this saw doesn't rotate, it actually vibrates and these vibrations cast are capable of cutting hard materials like plaster, but when it comes to softer and more elastic materials like skin, the small teeth of the blade cannot grip while vibrating, instead it pushes the skin back and forth.