This short poem from Clark Ashton Smith (CAS) was published in his hometown newspaper (the Auburn Journal) in 1923, but is not available on The Eldritch Dark, so here is the complete text:
Sudden, familiar, unbesought,
Like the quick pulse of some recurrent pain,
Your beauty comes again
To roam the weary spaces of my thought.
I see the smiling phantom pass,
And wonder if my darker soul has flown
To haunt your dreams unknown,
Or linger like a shadow in your glass.
As a poet of love and romance, CAS could be a little inconsistent, but "Exchange" captures his unique spectral sensibility and mixes it into commonplace memories of a past romance.