A circuit made from lemons, copper coins and galvanised nails. Lighting up a low-current LED.

The copper and zinc are electrodes, amd the lemon juice is an electrolyte. The acid in the lemon juice reacts chemically with the zinc and liberates electrons. These flow to the copper. Three of these electrochemical batteries in series is enough to light a low-current LED.

I mean this stuff is like woahhh. Absolutely fascinating!