I had to look this up, From Wikipedia: The diddley bow is an American string instrument of African origin. It is typically homemade, consisting usually of a wooden board and a single wire string stretched between two screws, and played by plucking while varying the pitch with a metal or glass slide held in the other hand.
The diddley bow is significant to blues music in that many blues guitarists got their start playing it as children, as well as the fact that, like the slide guitar, it is played with a slide.
A notable performer of the instrument was the Mississippi blues musician Lonnie Pitchford, who used to demonstrate the instrument by stretching a wire between two nails hammered into the wood of a vertical beam making up part of the front porch of his home. Pitchford's headstone, placed on his grave in 2000 by the Mt. Zion Memorial Fund, is actually designed with a playable diddley bow on the side as requested by Pitchford's family.
Recent performers who use similar instruments include New York City-based jazz pianist Cooper-Moore, American bluesman Seasick Steve, One String Willie, One String Sam, and blind musician Velcro Lewis. Jack White makes one at the beginning of the movie It Might Get Loud.
