Close encounters are the designation of three of the six categories of unidentified flying object in the classification scheme devised by J. Allen Hynek. A close encounter of the first kind (CEI) is any UFO reported to have been within about 500 feet of the witness. A close encounter of the second kind (CEII) is a UFO that leaves markings on the ground, causes burns or paralysis, frightens animals, or interferes with engines or TV or radio reception. A close encounter of the third kind (CEIII) includes a purported sighting of the occupants of a UFO. To these categories, ufologists have added two others. A close encounter of the fourth kind (CEIV) is one in which a person reports having been abducted (see alien abduction). A close encounter of the fifth kind (CEV) is one in which it is claimed that communication takes place between a human and an alien.