Demonic possession is very rare, but also very real, there is an exorcist right at this moment somewhere performing an exorcism.In Catholicism cases of demonic possession-in which demons battle for a persons soul,are dealt with by formal exorcism rites that date back to 1614.
The days of it being shrouded in secrecy,is still somewhat common.For the non believers its usually referred to as medieval superstition,but you may be surprised to know that the vatican has a vastly large army of exorcist priest in training, on an on going basis. Italy alone has about 400 trained exorcists, ready to do battle with evil.Exorcism by the catholic church, in this day and age, is taken very seriously.
Full demonic possession, happens when a persons body and will are taken over completely by a demon or demons.
it is believed that the "victim" must give some type of permission to the demon, before a full possession can takes place, either intentionally, or unintentionally. There is usually a long process, and the demon breaks down its victim's will a little at a time. Some believe, that certain laws exist in the spirit realm, some that demons must abide by and boundaries they cannot cross.
More common, and something that we see much too often as paranormal investigators is "oppression" or partially possesed, where someone is heavily influenced by a demon/ negative spirit, the beginning stages, weakening them and at times disorienting them.In this state, the victim,may show signs of a full possession,then return back to their normal state.
Negative or Demonic activity usually includes, black mists and masses , knocking rappings in threes, footsteps or hoof sounding steps through out the house.Scratching inside the walls,dark shadows, foul smells,hot/cold spots,unshakable feelings of dread ,deep depression,illness, religious objects may be desecrated, an atmosphere of pure evil, and phantom animals are just a few of the phenomenon that can occur.
*Some believe, "shadow people" are actually the gate keepers of Hell.
* The only goal of the demonic is to torture,harass and to destroy life.