many people would think that shattering glass is easy. But shattering glass with your voice is a whole different story. The act of shattering a glass with your voice has a huge backround that involves the physics of sound waves. First off, the glass in question needs to be crystal, not just any glass. The glass hums (and doesn't shatter) because the amplitude of the waves is not sufficient to surpass the strength of the glass. in order to break the glass you must porduce a sound that has the same frequency that the glass resonates at the glass should break. In an experiment that myth busters did, it showed that it is very hard to break a glass with just your voice but it is possible. before the glass shatters if you play in in slow mo or up close you can see the glass start to shift like jello. Its surface shakes and eventually (If you have the right tone) will shatter. Its amazing what sound waves can do!!!!!!!!!