Polecat to Ferret

[Blueberry]

New wild animal, polecats. Can be tamed into ferrets. Ferrets are kept in cages like chickens and rabbits. Once in a while, dead small animals will appear in the cages, their quality matching the ferret that caught them. If not taken out, the prey will eventually be consumed. Ferrets can also fit in the inventory. When dropped near small animals, ferrets will quickly hunt them down, then return to the hearthling that dropped them.

Stoats could be tamed into ferrets instead, since they're already in the game, but irl it's more likely ferret descended from polecats.