Clinking Coin

2L soda bottle
quarter
1 cup of water
1) Place empty soda bottle in the freezer for 10 minutes.
2) Remove bottle from freezer and immediately cover the mouth with a wet coin. Wet coin by dipping the coin in the cup of water. Explanation: When the bottle is placed in the freezer, the cold causes the air inside to contract, pulling in more air. When you remove the bottle from the freezer, the air expands. The coin clinks as one edge is lifted by the warming air, allowing it to escape, then falling.