I have been lost in an art book that I just got on an incredible sale
at Borders which has Lady with Ermine on the front.
 
Here are a few things I learned:
 
Did you know that there is another albino ferret piece (a pen and ink) of
his called "Allegory with Ermine" c. 1490 in the Fitzwilliam Museum in
Cambridge?  It illustrates an old belief that the creature will rather be
killed than sully its fur in dirty water.  This is why it became a symbol
of purity.  I guess that is why they usually hate baths -- the water is
never clean enough. ;-)  Another belief at the time was that they only
ate once a day (which is interesting since you'd think that someone might
have noticed that they apparently cache food like ferrets do and eat
leavings when desired but many other aspects of basic biology weren't
known then, either, and it far was harder to share information then).
 
Lady with an Ermine was done of Cecilia Gallerani who was the most
important and favorite mistress of Ludovico Sforna when she about 24 or
25 years of age.  It was done close to the time Sforna was due to marry
so it appears to be an allusion to their closeness despite his coming
union, and was given to her.
 
The ermine was a symbol of purity and modesty, but there was further art
punning.  The Greek word for ermine, Galee (Insert and accent mark over
the first "e" when you read, please, is similar to the young lady's
surname.  It was also a symbol of Ludovico Sforna, so was a safe way to
refer affectionately to him in her arms, while their echoing postures
refer to how close they were and how well they suited each other.
 
BTW, the animals in the painting and pen and ink are actually albino
ferrets rather than the smaller, more gracile, untame ermine.  That was
not mentioned in the book, but learned elsewhere and simply obvious when
the animals are compared.
[Posted in FML issue 4252]