The magician shows a penny and covers it with a block. Instantly, the penny shrinks to less than half it's original size - into a miniature penny. The block and mini coin can be immediately examined by the specatator and the secret will not be discovered.
This trick can also be used to change a penny into a dime - and again, all can be examined without fear of divulging the special secret working.
Easy to do and comes with step-by-step video instructions.