Why does a pickle light a light bulb?

According to an experiment reported at Exploratorium, a pickle can be used as an energy source to power small devices such as a light bulb or buzzer because of its ability to push and pull electrons. The pickle is high in salts and electrolytes, which can react to move electrons.

The described experiment requires a completed circuit, a graphite pencil to donate electrons to the circuit and aluminum foil to pull electrons away. Together with the pickle, these components can form an electron pump that sends high-energy electrons toward the light bulb in much the same way that a battery does.