The lost, roaming and restless spirits in our world seek sufficiently complex matrices to inhabit. To them the world of humans and animals is impenetrable, though they create much disturbance in the trying. Their desire to become substantial, to become whole again, is so powerful that they turn to other things: Chairs. Refrigerators. Appliances. Cars. Computers. And so delicate and intricate is their construction that they can only find adequate interface with those things that the Living perceive some level of randomness and chaos in. A little old lady in Muskogee has a spirit in her Victrola; I myself see Gods muster, rally, and die within thunderstorms.
It's a very subjective thing, and we are incapable of knowing our role in it. Best to not think about it, but knock on wood all the same.