Heads or Tails

Father and child ask another member of the tribe to spin a quarter on a table while your backs are turned and you will tell whether it falls heads or tails ten times out of ten. Secret: Make a notch on the edge of the coin near the head side, at an angle with a knife or file. Now spin the coin on a hard surface, such as a table and listen to the 'ring' as the coin stops. You will notice if you listen carefully that the ringing sound is longer when it settles head up than when it settles tail up.