The incredible paper cup

They show two empty paper cups. Put one of the two cups in a paper bag. Place the other cup on the table and crush it with your hand. 

But what happens now is magical: you hold the crumpled cup against the paper bag and suddenly you hold the intact cup in your hand. If you now get the second cup out of the bag, it is now suddenly crumpled up. 

You will receive paper cups (replacements are available from major distributors), an aid and 2 paper bags and brief instructions in German.