In 1994, I had the rare privilege of adopting a purebred Russian Blue cat. The breed is known for its intelligence, loyalty, and stubborn streak. By January, 2007, she was in full-blown chronic kidney failure, and deaf. IV fluids kept her healthy until this past week. I made the decision to euthanize her when she stopped eating and began to withdraw. Usually she demanded eye-contact and was very people-oriented, but hid her head and wanted no cuddles at all.
Combined with 3 days of no food and constant vomiting, the decision was easy - save her from having to shuffle in pain out of this world. I took her body home with me Tuesday morning. By Tuesday evening, I had a lively 3 or 4 year old cat bound through my home (she had died at 15-1/2). She jumps on my bed and pushes my feet out of the way, zooms up and down the stairs, and generally hangs out with me or my roommates. We don't see her per se, but we catch movements in the corner of our eyes and see flashes of cat shaped movement on the stairs. This is no demon entity, just my dear pet refusing to go to her rest. It isn't particularly scary, and we are getting used to the idea. The running joke is to reassure ourselves that there IS no cat in the house. We laugh and say yeah, right, and watch the flicker twist around our ankles just like she did before her body died.
Having a ghost cat isn't so bad. After all, it saves on pet food and cat litter. And vet bills.
About the passing itself: I was puzzled about her death, because it was so unlike my last cat. My little orange half-Siamese was put down and click! The lights were out, he was gone. He had been with me for nearly 7 years, was a mellow, sweet fellow, and he just turned off. I took his body home and nothing ever happened, though he was a kind and loving pet. With this one, the vet, the vet tech, and I all felt that someone left the room - Elvis has left the building indeed.
The room was emptier, I guess, as though a fourth person had left.