Bottle ghost

An empty wine bottle, which has been stored in a cool place, has a ghost in it!

Moisten the rim of the mouth with water and cover it with a coin. Place your hands on the bottle. Suddenly the coin will move as if by a ghostly hand.

The cold air in the bottle is warmed by your hands and expands, but is prevented from escaping by the water between the bottle rim and the coin. However, when the pressure is great enough, the coin behaves like a valve, lifting up and allowing the warm air to escape.