How was this food demonstration done?

I saw a food demonstration involving the lighting up a light bulb.
First the light bulb was plugged into an outlet. Another lead was placed into water. Nothing happened. Then this same lead was placed into Coca Cola and the light bulb lit dimly. Finally the lead was placed into a berry juice called MonaVie and the bulb glowed brilliantly.
The device may use an optical coupler between the 110 volt bulb and the test lead(its analog). The test lead may measure ions or conductivity of the beverages. Not sure