A Mighty Voice
A prophet is never without honor but in his own country, and few of your acquaintances will believe you to be such a wonderful person that with a single shout you can break a glass. Yet it is very easy to convince them.
Take an ordinary wine-glass, and hold it by its foot firmly to the table. Make the glass ring with a touch of the finger (it will probably sound a rather low note). While the glass is yet tingling, raise it rapidly to your mouth, and shout the same note that it rang full into the bowl with all your force. The chances are ten to one that the glass will shiver to pieces.
The reason of this phenomenon is the vibrations caused by the tingling are so suddenly increased by the strength of your voice that the glass is unable to bear the strain, and therefore breaks.