The whole song turns on one rhythm-guitar voicing and a bass that reharmonizes the same shape from underneath. The guitar holds G, A and D across every bar, the root and ninth and fifth of G with no third inside it. Over a G bass that shape works as G add9, and over a B♭ bass the very same three notes sound a B♭ six-nine.
The chord identity comes from the bass by itself. Two bars of G give way to two bars of B♭, a I to flat-three move repeated as the engine of the form. The fingers hold still while the harmony underneath flips from home to a borrowed flat-three.
This is the central trick stated in the first cycle. One stack, two chords, the bass doing all the work. The ear hears motion that the guitarist's hand never makes.
The rhythm guitar keeps its one voicing third-less all song. The G plus A plus D shape gives root and ninth and fifth and no third, which the audio-truth model confirms at two percent B against a wall of G, D and A. The voice walks in on the second cycle and supplies what that voicing leaves out.
Over the G chord the singer holds B, the major third of G, the exact tone the voicing omits. Over the B♭ chord the singer moves to C, the ninth of B♭, a bright color above the borrowed flat-three. One voice fills the gap the rhythm voicing leaves open, while the lead guitar keeps its own third alive higher up, which the next section takes apart.
The thesis matches the album opener almost exactly. The rhythm voicing gives a chord with no third and the vocal becomes the third. The Alligator builds its identity on that withholding by the rhythm part.
The lead guitar holds F♯ through the G sections, the major seventh of G, a high sustained tension over the home chord. When the bass moves to B♭ the lead stays inside G major and keeps that F♯ ringing. So the lead plays one key while the bass implies another.
That disagreement is the quiet engine under the riff. The bass says flat-three and the lead answers in the home key, a small bitonal rub on every B♭ bar. The B♭ section even stacks C and B and F♯ in the lead, a cluster pulled straight out of G major, and that B is the very third the rhythm voicing refuses, so the guitar does hold the third, only in the lead and only up high where it reads as tension. Read the album as two to four guitars, not one; each part stays inside a single hand's reach, and the thesis is about the rhythm voicing, not every string in the room.
The song keeps two tonal stories running at once. The bass walks its I to flat-three path and the lead never leaves home. The listener holds both readings together.
Every return from the B♭ section back to G flags itself in the bass. The player holds B♭ for most of the bar, then drops a fast three-step walk of B♭ to A♭ to G. The steps move in thirty-second notes, a quick chromatic slide into the downbeat.
The walkdown lives at the seams of the form, bars four and eight and ten. It is a small figure that stitches the flat-three back to home each time. The ear feels the pull of the chromatic descent into the G.
That tiny move gives the loop its forward motion. The two-chord engine could feel static across so many bars. The walkdown keeps shoving the form back to its beginning.
The chorus ends on a chord the rest of the song avoids. The guitar stack holds its shape while the bass walks G to B♭ to G and finally to B. On that last beat the bass gives B, the major third of G, the exact tone the rhythm guitar withheld for the entire song.
So the third arrives at the cadence, and it arrives in the bass. The voice supplied the third all the way through, and the final chord hands that job to the lowest voice. The G over B first inversion closes the phrase with the missing tone finally spelled.
The whole song pointed at this single low B. The rhythm voicing never fretted a third and the cadence finally gives one in the bass. The Alligator resolves by stating out loud what it hid the whole time.