The poem is a set of five short comparisons, each built on the same pattern: guitar uses one word, banjo answers with another. The guitar's vocabulary is the familiar, polite language of instrument parts: body, soundboard, six strings, bridge, hole. The banjo's replies shift things in a stranger, more physical direction. A body becomes a head. A soundboard becomes a membrane, since a banjo's sound comes from a stretched skin. "Six" becomes "one for each finger," which loosens a fixed number into something personal and handmade.
The last two lines are where the poem turns. "Bridge" becomes "keep going," so a part of the instrument turns into a kind of instruction, almost a way of living. Then "hole" becomes "full," the sharpest reversal: the guitar's emptiness is the banjo's presence.
The speaker seems to side with the banjo, though the tone stays playful rather than argumentative. The mood is dry, affectionate, and a little cheeky, like a joke that quietly becomes a small philosophy.