I'm sure this has come up before, sorry if it's an obvious question. Noticing this a lot when transcribing walking lines, the bass often outlines a minor chord over a dominant by playing the minor 3rd instead of the 'correct' third. A good example is Paul Chambers on Warne Marsh's Yardbird Suite, he does this during the head over the D7 several times. I'm wondering if this is just 'because it adds tension / interest', or whether there's more thinking behind it, especially as he only does it over that specific dominant chord, not so much the others. My theory: in the A section of this particular tune, the chord that follows the D7 is a G7, so is he implying a II-V-I by playing a minor third there? Would make sense as the tune is in C. It's interesting that this works so well in context even though the chord it's under remains a dominant.