I was thinking about "I Want Her She Wants Me" last week, and I realized that one section of the bass part at the beginning of the song is similar to a section of the bass part in "Summertime."
Notating the bass part in the introduction to "I Want Her She Wants Me" is still beyond me, but the first few phrases fit nicely in 3/4 (the majority of the song is in 4/4, though):
where the first G in each measure is a hammer-on.
In "Summertime," there are some very similar phrases, first occurring at ~0:23, under the "high" of "and the cotton is high":
where the first E in each measure is a hammer-on.
The interval between the two pitches in "I Want Her She Wants Me" is a half-step, and the interval between the two pitches in "Summertime" is a whole step, but otherwise, these figures are the same. In both songs, the figure also occurs three times in succession.
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This similarity between the bass parts reminded me of a similarity between the backing vocals that I noted years ago. I revisited the parts and improved my accuracy, but I'm still not sure I have everything note-perfect.
The backing vocal in "Summertime" is something like:
It's a bit different the second time. Instead of just E F# in the last line, the E F# G# F# figure is repeated.
The backing vocals in "I Want Her She Wants Me" are something like:
Common to both is the sequence E F# G(#) F# in fairly even note values.