When my cat Tiger died she left a nearly unbearable ache in my heart. Animals do this: They hold joy and love and solace in a way humans can’t, and then they die. But after she died, I heard her. I was sitting at my desk and the sounds of her nails tap-tapping down the wood floor of the hall came to my ears, and only when I turned to look for her did I remember that she was gone. Sometimes I felt her presence, like a heaviness on my lap or at my side. Sometimes I still do.

It turns out that this is not uncommon. As many as 80 percent of those who lose loved ones report that they sense that person after death. These are real sensory events. People hear a voice; they feel a touch; they recognize a presence. A friend told me that a year after her husband’s death, she would still find him sitting on that bench in the park, waiting for her. She liked that. In fact, one of the central research findings in this area is that post-bereavement experiences are helpful. They’re also more likely to occur after long and happy marriages. (There appears to be no research yet on pet loss.)

One study found that one in 10 people had sensory experiences so rich and frequent that they felt their dead spouse was always with them. “Part of my life is gone,” Dame Thora Hird, a British actress, told The Daily Telegraph in 2000, about the loss of her husband after 58 years of marriage, “but he isn’t a long way away. Don’t think I’m being silly, but I sit in his easy chair in the loft and so often, I have a feeling he’s there.”

Our ancestors thought that the dead could walk and speak with us. That, of course, is the point of Halloween, or Allhallows Eve, the time of year when the veil between the worlds was thought to thin. The day probably descends from one of the great fire festivals celebrated by the Celts, All Hallow Even, the day when the souls of the departed would visit their old homes and warm themselves by the fire. “It was, perhaps, a natural thought,” Sir James George Frazer, a Scottish anthropologist of the Edwardian era, wrote in his magisterial “Golden Bough,” “that the approach of winter should drive the poor shivering hungry ghosts from the bare fields and the leafless woodlands to the shelter of the cottage with its familiar fireside.”

Of course, it was not only the dead who roamed on that night: “Witches then speed on their errands of mischief, some sweeping through the air on besoms” — or brooms — “others galloping along the roads on tabby cats, which for that evening are turned into coal-black steeds.”

We tend to treat this old folklore as so much fluff — the stuff of masks and costumes — but increasingly, scholars are finding evidence for its experiential underpinnings. Another example of a real psychological event that may partially explain our folklore is sleep paralysis. A quarter or more of all Americans report that they have awaked to find they cannot move. Often they feel a weight on their chest, hands clutching their throat and a dark malevolent presence in the room.

“I was a college sophomore,” one man recalled. “One night I went to bed early. I was awakened by the sound of my door being opened, and footsteps approached the bed. I tried to turn on the light beside my bed, but I couldn’t move or speak. The footsteps came to the side of my bed, and I felt the mattress go down as someone climbed onto the bed, knelt on my chest and began to strangle me. I had an overwhelming impression of evil. And then I did move, first my hand and then my whole body. I leaped out of bed, heart racing, and turned on the light to find the room empty.”

To be sure, the fact that we can identify in-the-body phenomena (hallucinations, sleep paralysis) associated with ideas about the supernatural does not necessarily mean that those ideas are false. Mr. Hufford, who also studies near-death and other remarkable experiences, is very clear about that: “Learning as much as we can about spiritual experience does not make spirituality go away.”

But what this research makes clear is that when people report that they hear their dead husband or are terrified by an evil presence that groped at their throat in the night, they are not necessarily making it up, nor are they crazy. Events like these are rather what Ann Taves, professor of religious studies at the University of California, Santa Barbara, calls the “building blocks” of religious experience. The experiences are psychologically real events. How you interpret them is up to you.

Happy Halloween.