The Z.Vex Fuzz Probe is bar none one of the wackiest pedals ever devised. Think of it as a cross between a theremin and a Fuzz Factory. There's an antenna plate mounted on a chunk of acrylic that passes over the top of the pedal housing. It 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). This lets you select your fave FF settings and then mess around with the STAB setting with your foot and create little melodies and interference modulations with your guitar.