Ok, I have recently been watching Brainiac, because they are showing it on a channel which, until they started showing this show, I had a self-imposed boycott on. Anyway...
They did a bit where Dr Bunhead crushed a can with air pressure.
Here's how it was done:
Bit of water inside a coke can.
Bit of water in a tray - maybe an inch or so deep.
Heat the bottom of the coke can until steam comes out.
Quickly invert the can into the tray of water.
The can collapses.
I wanted more information, and I found this: www.delta.edu/slime/cancrush.html
That's all.