Shadyside resident Estelle Meyer says she has two pets.

There's Chloe, a kitten she took in last year after it was tossed out of a car window. She feeds, hugs and plays with it, as would any loving pet owner.

Then there's Winnie.

"Bye, baby. Momma will be home later. You be good girl," the 73-year-old tells Winnie daily when leaving for work. Upon returning, it's "Momma's home!"

Winnie is the name of Ms. Meyer's beloved dog, who died in January 2006. But she believes her dog's spirit lives on and continues to visit her home.

"Every now and then I hear her coming up the steps. I can sense her, feel her. She was the most special, special dog. I loved her to pieces," she said.

Ms. Meyer is not alone.

Many pet owners report seeing, hearing, smelling or feeling the presence of their beloved pet after its death. It can be an apparition of Fluffy lying on her favorite rug or the faint clickity-clack of Sparky's paws traipsing down the hall. Other times, it's the distinctive odor of Fido's fur.

Sometimes more than one family member acknowledges seeing the pet.

Debra Rightley of Mars, whose 13-year-old Afghan, Elsa, was put to sleep when Ms. Rightley was 12 and living in Whitehall, remembers appearances beginning two months after the dog's death.

"My favorite visit is one that I only recently, as an adult, learned my mom also witnessed," she said.

On that occasion Ms. Rightley, now 38, and her mother, Carol Jakub, were in the living room. "I saw Elsa come from the dining room and go down the hall to my parents' room. Their door was closed, but in typical Elsa fashion, she used her nose to push the door open -- just enough to poke her head through -- and she disappeared."

Although Ms. Rightley didn't say anything at the time, a few years ago her mother also admitted seeing the same thing.

"I'm comforted by the fact that she was never really gone," the daughter said about Elsa.

Is it possible for a dead pet to scamper between worlds? Does anyone really know? What's behind the phenomenon?

Dr. Mark D. Miller, an associate professor of psychiatry at UPMC's Western Psychiatric Institute and Clinic, said his profession generally views reports of pet spirit encounters as nonpathological, grief-related hallucinations.

It's very common for people to have friendly hallucinations of deceased relatives, he said. About 50 percent to 80 percent have them at least once in the first year after a death.

"It's on an unconscious level. We really think it's a phenomenon where the critical thinking part of your brain is suspended, because you want to believe so much that, yes, maybe they are coming back, maybe they aren't really dead," he said.

Pet owners can have similar types of hallucinations, especially if they were really attached to the pet, he said.

"But the phenomenon is in the mind of the observer, not in an actual visiting of the pet," said Dr. Miller, who also is board chairman of the Good Grief Center for Bereavement Support in Squirrel Hill.

Psychologist Wallace Sife, founder and board chairman of the Web-based Association for Pet Loss and Bereavement (www.aplb.org), said when grieving pet owners hear or see things that are not there, they're not crazy, and there's nothing paranormal about it.

"They're not accepting the pet's death. They are not accepting the reality because it's too painful. Hanging onto the pain is, in a way, hanging onto the pet," he said.

Dr. Sife said bereaved pet owners talk about pet spirits all the time in his organization's chat rooms. Those who truly believe in the hallucinations often are in denial and delaying their healing, he said.

Healthy grieving requires accepting a pet's death both intellectually and emotionally, and bereavement counseling can help with that, he said.

Carey K. Morewedge, an assistant professor of social and decision sciences at Carnegie Mellon University, said it's "incredibly implausible" for pet spirits to exist because there's no hard scientific evidence to support the notion. But social psychology does offer explanations, he said.

People tend to anthropomorphize things in their environment -- which means they attribute human personality, form or thoughts to things not human, he said.

Scientific evidence has shown, too, that when people are lonely, they are more likely to anthropomorphize their pets and, when thinking about death, are more likely to believe in supernatural entities.

"So, if people are thinking about their dead pets, they may at this time be particularly likely to believe there are spirit animals. Unfortunately, it's probably more likely these kinds of experiences are misinterpretations of different types of sensory experiences," Dr. Morewedge said.

Not all agree. Pet spirits absolutely exist and visit their owners, said Janice Dreshman, a registered psychic medium in Lily Dale, N.Y., a spiritualist community. She also has a medium practice in Pittsburgh.

"In my experience, those pet owners are being able to witness a piece of Spirit." She defined Spirit as the purest light from God or The Divine that is a part of every person and animal.

When a pet passes, she said, its spirit "can choose to be happy, joyous and free" and return in a vibrant and healthy form. Even though its physical body dies, its spirit, soul, energy, consciousness -- whatever a person chooses to call it -- continues to live on, said Dr. Dreshman, an ordained minister in the Fellowships of the Spirit church in Lily Dale.

Morningside resident Lee Nesler said she's had a handful of animal spirits visit her over the past several years.

"I've rescued a number of end-of-life animals from a local shelter, and they've maintained a companionship with me in the spirit world," she said.

For example, a spirit dog sometimes appears in outline form and "zips around the yard and house acting like a hooligan, like a dust storm," she said. A spirit cat, also in outline form and with its calico pattern, will appear on her mantel, she said. And a "hazy shadow" of her pet dog, Tag, who died seven years ago, once appeared by a tree in the backyard.

"I think they come because my home is something familiar to them and they're welcome there. And I think the end-of-lifers were very grateful to have a home after the situations they were in," Ms. Nesler said.

Renee Takacs, of Mars, who calls herself an animal communicator, said a pet spirit can feel its owner's grief after its death, and can come back to ease their owner's pain. It doesn't return because it misses its owner, she said.

"In my experience, when an animal crosses over into spirit, there's usually such a sense of relief and freedom that only love exists then," she said. "They will come back from the spirit realm to visit their person because of the loving connection, not because of a lower vibrational emotion like sadness."

Whether pets can visit their owners in spirit depends on whether they have an afterlife.

It's a complicated subject that's not at the forefront of religious discussions, said the Rev. Kimberly A. Rapczak, one of several local clergy who host pet remembrance services at Animal Friends, the no-kill shelter in Ohio Township.

There are people who would believe in the existence of animal souls and their survival beyond death, but not all of those people would believe that an animal's spirit could come back to visit, she said.

For example, Joe Hirsch, chairman of the Hearts and Paws Ministry at Christ United Methodist Church in Bethel Park, said he believes animals have souls, but he doesn't believe in the paranormal. In his view, a belief in pet spirits comes from grief and a memory connection.

He said he thinks about his recently deceased cat, Miracle, all the time. It's a fresh wound, and sometimes at night, he reaches out next to his pillow to pet her. "That's not a paranormal experience. It's just my looking for what is missing, similar to people who lose a limb and still feel it's there, that kind of thing."

The Rev. Rapczak, a Lutheran minister, said a lot depends, too, on whether an individual believer accepts the official teachings of their religion.

She said, to her knowledge, no Western faiths officially teach the survival of animals beyond death. "They teach that when animals die, they die."

Eastern faiths such as Hinduism and Buddhism have different views where, for example, animals fit into the great wheel of reincarnation, she said.

The Rev. Ronald Lengwin, spokesman for the Catholic Diocese of Pittsburgh, said the Catholic Church does not know much about eternal life other than it will be spent with God.

"Some theologians would say animals will not be in heaven; some would say absolutely they will. We think that everyone who owns and loves a pet, and is loved by a pet, believes they will be in heaven with them, but we just don't know," he said.

Don Wagner, founder and tech manager of the Peace of Mind Paranormal Society in Finleyville, Washington County, said anybody who's truly into the paranormal will say animal spirits exist.

His team doesn't get many requests to investigate pet ghosts, presumably because pet owners want the visits to continue, he said. But when the society does take on a pet ghost case, it works to make sure the ghost isn't a hallucination caused by such things as carbon monoxide, mold, high electromagnetic fields, antidepressants, or emotional or psychological issues.

Years ago in the North Hills, the society captured audio evidence of a suspected ghost cat, Mr. Wagner said. The client said something would shake her mattress each morning, jump on her chest and purr loudly in her face, waking her up. Her pet cat died long ago. The team heard the purring while sitting in her kitchen.

"We were hearing it and recording it. It was unbelievable. We were looking at each other like, 'This can't be happening.' We could not find anything causing it," Mr. Wagner said.

Joshua P. Warren of Asheville, N.C., author of "Pet Ghosts: Animal Encounters from Beyond the Grave," said people around the country report animal apparitions all the time. He calls them "phantimals" -- a mix of the terms phantoms and animals.

"We can easily say that thousands of people have experienced the spirits of deceased pets and animals. However, these phenomena have been poorly investigated from a scientific point of view; therefore we cannot know what percentage of them are credible," he said in an e-mail.

The bottom line is, while there are many case files presenting anecdotal evidence of pet ghosts, there's not enough consistent data to warrant true scientific proof, Mr. Warren said.

"When and if that day arrives, the subject will cease to be 'paranormal' and will become 'normal,' " he said.