In Wicca, or at least in the StarKindler tradition, the Great Work is the initiation of life to higher consciousness.
In particular, we hold that the animals we keep as pets and companions will, through contact with us, become more individual and less "just an animal". They won't become fuzzy human beings, but they become individuals and are no longer part of a group soul. Eventually, animals become sufficiently individual that they reincarnate as sapient beings with their own unique souls. They become initiated into individual consciousness.
I've seen a few cases now where an animal will come in to a household, and die very young from some disease or genetic condition. (My high priestess had a mastiff that died at under a year of age, because his immune system had never been properly installed.) I've decided this is a case where the animal is "picking up the last few credits" before moving on to the status of unique individual.
Yesterday, Simon, the white cat with gray patches in joansteward's household, had to be put down. The vet said tests had found ten different conditions that were not compatible with life, and offered to waive the cost of euthanasia. He'll be missed.