The copper antenna of the ZVex Fuzz Probe projects a field of RF energy that is affected by your foot (or other appendage), altering the circuit that generates it, and in so doing, increasing the brightness of that LED on the top of the pedal and also controlling the STABILITY (STAB) knob on the back. Its connected to the stability knob too. This lets you select your favorite squealy fuzz factory setting and then mess around with the STAB knob with your foot and create little melodies and interference modulations with your guitar.
* This pedal is HAND PAINTED, as such no two will be EXACTLY alike. Your Hand Painted Fuzz Probe may differ from the one pictured.