Notice the abundance of imitation in "My Melancholy Baby," particularly in bars 20-21 of the first chorus, bars 1-4 and 11-13 of the second chorus, and bars 17-19 of the third chorus.
"It's You Or No One" exhibits imitative playing as well, for example in bars 16-21 of the second chorus. Indeed, Lee and Warne are so highly attuned to each other that they converge on an identical melody in bars 31-32!
Also note the cross-rhythm that emerges in bars 16-21 of the second chorus of "It's You Or No One" as Warne and Lee each play 3:4 polyrhythms that are out of phase with each other by one beat. (Warne's polyrhythmic figure starts on beat 4 of bar 16, completing two full periods just as Lee's starts on beat 1 of bar 18.) Despite the rhythmic complexity, this passage shows rather harmonious 4-3-6-5 voice-leading.