The bass part isn't very unusual for its era, but there are two features that I found interesting.
For most of the song, the bass arpeggiates the chords it's played beneath. There's the root, third, and fifth, and then it adds a sixth and a flatted seventh before descending, playing the same notes in reverse order. This is a standard feature in early rock and roll bass parts. However, underneath the Bb major, the bass forgoes the flatted seventh and instead plays the root an octave higher. Instead of
which would match the figures played underneath the F major and C major chords, it's
Musically, it makes the song more interesting, but it also demonstrates the character of the snake. This musical figure doesn't match the others in the same way that the snake seems to challenge authority and do whatever he likes. For three of its four occurrences, the lines above this figure describe the snake: "He tracks her down on the way to school," "And he wants to go and have some fun," and "And he's thinkin' 'bout his recreation." The only line above this figure that doesn't mention the snake still has a sort of rebellious element in that it features grammatical errors and mentions the possibility of failing a test: "Well, she got a test, and she don't wanna fail."
At the end of the instrumental section, the song changes keys from F major to F# major. This is a musical illustration of what happens in the third verse:
The snake got the bookworm one fine dayAfter he kisses the bookworm, the snake becomes a bookworm himself, and in order to match this change in his character, the song changes keys. I think there might even be a bit of a musical joke here. The key changes from one flat to six sharps. It becomes "very sharp" in terms of note accidentals, but "very sharp" could also describe an intelligent person, like a bookworm.
And he wouldn't let her get away
Mm, and then he kissed her just one time
And then something happened to his mind
Well, now he sings a different song
He's a-been studyin' all night long
The snake is a bookworm
Similarly, the bass figure underneath the B major chords (formerly Bb major chords) now matches those underneath the F# major and C# major chords. They're all root, third, fifth, sixth, and flatted seventh. Because of the snake's change, the earlier "rebellion" of replacing that flatted seventh with the root played an octave higher has disappeared.
Here's the bass part in full, with the disclaimer that - as always - I might have something wrong:
The other recording of "The Snake and the Bookworm" in my collection (from a compilation titled Essential Early Recordings in The Primo Collection) has the same structure, but it doesn't replace flatted sevenths with roots played an octave higher in the first two verses and, instead of the string of F# notes near the end, continues the arpeggios.
The chords are the same for both versions. It's almost a three-chord song, but in some spots, there are rapid changes to the chord a fourth higher. Each line here represents two measures. The middle chord in each group of three is played for only one beat: the second beat of the second measure.
Introduction:
|: F major | Bb major | F major :|
Verses and Instrumental:
|: F major | Bb major | F major :|
|: Bb major | Eb major | Bb major :||: F major | Bb major | F major :|
C major
Bb major
|: F major | Bb major | F major :|
Verse after key change:
|: F# major | B major | F# major :|
|: B major | E major | B major :|
|: F# major | B major | F# major :|
C# major
B major
|: F# major | B major | F# major :|