An impossible and novel, visual revelation!

You place a beer cap on a spectator's palm, and then they pick a card.

After showing the cap on both sides, you place the cap on the card. Now give with touch the cap with your finger and the cap will fly through the air and fall again on the card revealing the chosen card inside the cap!
 
 
Easy to do
 
 
No changes
 
 
No chemicals
 
 
Fully examinable
 
 
Easy and fast to build
 
 
Cheap to make
 
 
Everything is self contained within the cap