No list of phenomena would be complete without mentioning the poltergeist.
The word poltergeist comes from the German words poltern - "to knock" and geist meaning "spirit" or "ghost". This phenomenon has been researched extensively for years and as a result there are a few different theories on what poltergeists are.

The following theory is probably the most popular.

A typical poltergeist haunting seems to consist of noises and objects being moved or moving about on their own. Voices, smells and apparitions may also be reported as being symptomatic of poltergeist activity. The activity often starts slowly with small noises and small objects moving and then may progress to the likes of flying furniture and full bodied apparitions. The exact events differ from case to case as well as the progression and severity.

Normally there is one person who seems more targeted than any other and this person is always present in the location when events occur. When that person is removed from the area, the activity will quieten or even completely cease.
Let me at this point draw attention to the difference between a poltergeist entity and poltergeistal activity. Smells, noises and things being moved are by themselves evidence of poltergeistal activity. Its when these events all occur in the same place and seem to be directed at a person or even a complete family that it should be attributed to a poltergeist entity.

It is not unusual for the focus of a poltergeist to be a preteen female "whose hormones and stress of that age have combined to release subconscious energy". Now as a sceptic I have to say this is all well and good, but how does this allegedly happen?

The centre of activity is often unaware that they are the cause, their removal from the scene can allow the activity to cease, their arrival back may have no effect or no immediate effect, but it is far from unheard of for the activity to restart and in  some cases with a vengeance. Attempts to remove the reasons fro the stresses in the first place may have a more beneficial effect.

Poltergeists are not always easily discernable from intelligent haunting's. The symptoms are often very similar and an onsite investigation and extensive research is often necessary to uncover the hidden existence of this type of phenomenon. This explains why many questions that investigators ask seem off base when they interview witnesses in a home. They are trying to rule out a poltergeist problem before they start the investigation into the possible spirit activity.