Jim - this was the first explanation of it I had heard of:
When people spun their own wool for weaving they used a yarn winder to measure the yarn into a skein. When the wheel went around enough to wind the length of the skein the yarn winder was geared to make a "popping" sound. This let the person know that the skein was finished winding. The name of the winder was "weasel."
However - there are some other versions floating around since "to pop" probably means to pawn something and the reference in one of the verses seems to be to a tavern that is still around
Of course there's also the explanation that it was a toned down version of a more "erotic" story/song
