haunted Tubes in London? In it they covered this guy who was doing experiments with Infrasound or low-frequency sound waves. The theory is - it is thought that these low frequency sound waves produce feelings of uneasiness, cause auditory and visual hallucinations and even cause people to feel chilled.
I grew up in a very haunted house and was always amazed that science didn't explore this phenomenon more closely. I am not sure that this is the complete answer but was encouraged to see someone actually positing a solution that is plausible. It doesn't account for simultaneous sightings or sightings of the same phenomena at different times by different people. But still - fascinating. Wouldn't be surprised if the answer isn't the other way around - this phenomena is causing the low frequency sound waves. More info here:
http://en.wikipedia.org/wiki/InfrasoundThat would explain why dogs and cats 'see' stuff we sometimes can't.
Thanks for the thread. Was looking for the ghost thread Friday evening - missed it then.