I'm grateful to Louis Cardell-Ree for pointing out that there is indeed a stand-up bass on this track as well as Danko's electric bass. 'William E. Lee' had been listed in Michael Krogsgaard's notes for this session, drawn from the studio records, but Lee had never been mentioned in any album credits, and his contribution was not an audibly obvious one as the two basses largely play the same notes.  

This style of 'tic-tac' bass, with an electric bass (or sometimes a baritone electric guitar) doubling an upright bass, emerged in Nashville in the late 1950s, where country music producers like Owen Bradley wanted to make bass lines more audible on low-fi audio equipment which couldn't adequately reproduce the traditional stand-up bass. The clicky top end of notes played with a pick on a bass guitar would cut through even on a cheap transistor or a car radio.  A nice example is Patsy Cline's "Crazy", where the stereo mix even has the two bass parts on opposite sides. Tic-tac bass was also used on many of the Beach Boys' 1960s recordings – check out "Sloop John B" for one.

Here on "One Of Us Must Know", the electric and stand-up basses do occasionally diverge: For example, Bill Lee plays a different note (C) than Danko (F) at 0:19, just before the vocal line "You shouldn't take it so personal"; and in the lead-in to the choruses Danko plays quavers while Lee generally plays crotchets (twice as long). This is all most easily heard on the separate guitar and bass track (or 'stem') for this song that was included in the Collector's Edition of The Cutting Edge.  For those who don't have access to that gargantuan release, you can listen to it in the Jam Session area of bobdylan.com's Studio A Revisited Micro-site: having chosen this song, all you have to do is select the guitar and bass stem (green blob) and then keep the volume right down on the other three stems. And while you're listening, you may notice that the "Did you know?" snippets that appear somewhat randomly during the song mention both Rick Danko and Bill Lee as bassists, even though the credits in The Cutting Edge listed only Danko – and of course neither was included in the Blonde On Blonde album cover credits).