I haven't seen a ghost, but I've experienced what could very well have been a Poltergeist.
While my late father read "ghost" stories to the family in the living room, something dramatic happened in the facing dining room.
My 3 brothers, mother and I were listening to my father read the true story of a man who had been sitting in his office at work, talking with a co-worker when all of a sudden, the glass ink well his sister had given him cracked down the middle, spilling ink all over the place. Two hours later, the man received a phone call that his sister had died two hours earlier. Later, he had the glass ink well analyzed and found that it had cracked against the grain. In other words, it was an unnatural break.
That's the story he had read, but when he got to the point where the ink well cracked, the glass cover of the light fixture above the dining table cracked. Amazingly, it didn't fall. It merely sat there, caught on a sliver of glass. Gingerly, my father lifted the bulk of the glass cover and lowered it safely to the table. What was left was a small donut of glass right at the decorate nut which held the cover in place.
Coincidence? Some coincidences are accidental. What are the chances that a glass fixture would break in a neat little ring around the nut and not fall? What are the odds that such a breakage would happen right at the breakage in the story being read?
Some coincidences are cause-and-effect.