An Ebow gives continuous sustain to a guitar string by creating an electro-magnetic feedback loop using two coils aligned with the guitar string and a small amplifier. The grooves on the foot of it are to help align the coils with the string. The input coil senses the vibration of the string (exactly like a pickup on an electric guitar), the amp chip amplifies the signal and sends it through the output coil which causes the string to keep vibrating. It "self-tunes" the amp to the amplified signal and becomes an oscillator that includes the string in the feedback loop. It works really well and is a very simple circuit. Is not anything like the slide guitar effect with a glass or metal slide. You can use them together though, and that's pretty cool sounding too.