Scotch & Soda by Katzini

The most popular coin trick of all time. The magician explains that the Centavo is smaller than the Half Dollar. The two coins are handed to the participant and they are asked to hold them behind their back with one coin in each hand.

Magician asks for the half dollar which the spectator successfully hands over. Next you ask for the 20 Centavo. He can't hand it over because it's changed into a quarter.