Effect:
A metal can with a screw lid is heated on a hot plate until some steam comes out. The cap is screwed on tight and the can is immediately removed from the heat. The can is slowly crushed by some invisible force.

What You Need:
- An empty can that has a screw cap lid.
- A hot plate
- Water
- a heat resistant pad
- insulating gloves.

What You Do Before the Show:
- Make sure the can is clean and empty.
- Put some water into the can.

What You Do During the Show:
- Put the can onto the hot plate.
- Turn on the hot plate.
- Let the water come to a boil and you see steam coming out of the top.
- Tightly cap the can.
- Remove the sealed can from the heat.

What is Happening:
The air in the can is displaced by the boiling water. When the can is sealed and removed from the heat, the water vapour inside condenses and the pressure drops. The can is not strong enough to resist the relatively increasing pressure of the atmosphere outside.

Hazards:
- The metal can will be hot and there will be scalding steam coming out. Wear heat resistant gloves.
- After sealing the can, immediately remove it from the heat, otherwise the increasing internal pressure may cause it to explode.
- Set the can down on a heat resistant pad.
- Turn off the hot plate.

Patter:
You pretty well have to make up your own depending upon whether this is a scientific explanation or just a trick.