We've talked about this before: ermines are the white phase of the weasel/stoat family. Their white fur made for a fine luxuriant trimming of noble robes. The House of Lords in Great Britain still sport "ermine" trimming on their robes, but these days, I am happy to report, it is faux. The ermine was also used as symbolic shorthand for the purity and innocence of the wearer. Though not much found in households now -- in favor of the more docile ferret, a very closely related species -- they served in times past as workers and pets.
You will see this illustrated nicely in The Medieval Ferret, or Ferrets in Art History, a well assembled page with extreme ermine/ferret close-ups of each work!