I was in a rock/funk/soul band that covered this many years ago. Always loved that one part, you know which part I mean.
If this is not the most soulful thing in history:
The basic idea is simple. The “I Know” figure is three sixteenth notes long. “I” is one sixteenth note, and “know” is two sixteenth notes. That odd-length figure goes in and out of sync with the sixteenth-step pattern underlying the rest of the groove. It’s a simple polymeter, but the execution is hair-raising. I made a seamless three minute loop of it if you want to hear it. RIP Bill Withers.