Much higher up:

Pop is clearly to pawn

But not pawning the heavy 'iron goose' used by tailors, but as was the tradition the man's suit was worn only on Fridays/Saturdays so the inference is that on Monday the suit was pawned until needed the following Friday/Sat after the man got paid and could redeem his pledge

Pop goes the Weasel = Pawning the suit until needed next weekend!

In my opinion
Ray