Long time investigators of the paranormal know that reports of UFOs, hauntings or cryptids, such as Bigfoot, go through cycles. When many reports come in from a particular location, that area can be said to be experiencing a cluster of phenomena.
Times of peak activity in such cluster regions are known as flaps. This terminology was developed by John Keel and other researchers who discovered that reports of variant kinds of paranormal activity tend to both cluster and peak together.
Keel and other investigators, such as Berthold Schwarz and Jacques Vallee, have also found that during periods of apparent decline in cluster regions, paranormal activity that continues to be reported often takes on a more complex quality, something which Keel, in particular, found very interesting.
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