The speaker starts by listing everything that doesn't frighten him: snakes, pigs' feet, bears, even the devil, whose temptations he says he can invent perfectly well himself. It's a joking, swaggering opening, but it sets up a surprise. What does shake him is a banjo.
He compares it to a clock, "lonesome" but with two fast hands, and then peers into its open back like someone opening a watch. Where are the gears, the escapement, the balance wheel? Instead he finds only a bare rod and "the smell of rain." The mechanism he expects isn't there, and the music seems to come from something unseen, a "ghost in its machine."
The mood shifts from wry humor to wonder and longing. The last lines sound like a voice urging someone on: play it, make it ring and rattle "until it smokes." The poem ends in noise and heat, suggesting that the banjo's mystery is something to feel, not take apart.