They fed 20,000 volts across the electrodes and locked tape recorders in the room for four hours. It was mentioned a few years back that the stones in the wall contain may contain similar substances to those found in modern tape. Again, this is sometimes real and is measureable on a thermometer, and other time it seems to be a perceived effect. One idea is that the ghost is somehow extracting energy from the air. How all these enviromental effects affect, or are affected by ghosts is an open area for research.
Dogs often bark at the air, and cats purr as if stroked by invisible hands.
In a similar fashion, John Spencer once related a theory that stated that ghosts seem to have a prediliction towards appearances when the witness is least expecting it, and hardly ever during vigils. But has anyone ever considered the effects that the introduction of equipment has on the appearance of ghosts- maybe the electrical and magnetic fields reduce the probability of a presence. In the Australian Humpty-Doo case, the Poltergeist would only put on a show once the TV cameras batteries had run out of power, and any witnesses had left the building. This implies that humans need to be present for manifestations to occur. Clearly this is not the case.