Counterintuitive Reaction of Aluminium On Steel Balls
This is actually related to the thermite reaction, where the rust on the balls reacts with the pure aluminum in the foil. Here is a pdf detailing the experiment.

The activation energy for the reaction is reached through the friction and pressure, and the rust on the balls is actually very important, since it is the exchange of oxygen between the iron oxide and aluminum that releases the heat as iron and aluminum oxide form.