Ah yes, the memorable 'Shoveling Shit Tour' of 2012. Who can forget it!
I believe they dedicated it to Obama's reelection.
This is an electrified version of something you used to see a lot of down south, sometimes called a 'diddly bow' or a box guitar because the normal bodies on the old ones were made out of a cigar box (they were mostly wood back then, although cardboard got used too) and some kind of thing like an old broomstick.I remember one where the guy had used an old faucet as a tuning key. Some of the old guys still have 'em and play 'em if you know where to look...
There's a similar instrument in the Arab world called a rub-abub with the same principle..one string, no frets and a sort of drone sound to accompany a vocalist or play melody lines.