|The 2013 Awkward Moments Children's Bible humorous rendition of Mark 5:1-17 by Horus Gilgamesh. |
In 435BC, Herodotus recounted the Egyptian superstition of running crazily into a nearby river after touching pig as follows: 
“The pig is regarded among them as an unclean animal, so much so that if a man in passing accidentally touch a pig, he instantly hurries to the river, and plunges in with all his clothes on.”
In c.150AD, the anon author of Mark 5:1-17, of the Bible, reformulated this Egyptian "pig-touching river-running" reaction craze, in a reverse manner as follows:
1. And they came over unto the other side of the sea, into the country of the Gadarenes. 2 And when he was come out of the ship, immediately there met him out of the tombs a man with an unclean spirit, 3 Who had his dwelling among the tombs; and no man could bind him, no, not with chains:
4 Because that he had been often bound with fetters and chains, and the chains had been plucked asunder by him, and the fetters broken in pieces: neither could any man tame him. 5 And always, night and day, he was in the mountains, and in the tombs, crying, and cutting himself with stones.
6 But when he saw Jesus afar off, he ran and worshiped him, 7 And cried with a loud voice, and said, What have I to do with thee, Jesus, thou Son of the most high god? I adjure thee by god, that thou torment me not. 8 For he said unto him, Come out of the man, thou unclean spirit. 9 And he asked him, What is thy name? And he answered, saying, My name is Legion: for we are many. 10 And he besought him much that he would not send them away out of the country.
11 Now there was there nigh unto the mountains a great herd of swine feeding. 12 And all the devils besought him, saying, Send us into the swine, that we may enter into them. 13 And forthwith Jesus gave them leave. And the unclean spirits went out, and entered into the swine: and the herd ran violently down a steep place into the sea, (they were about two thousand;) and were choked in the sea.
14 And they that fed the swine fled, and told it in the city, and in the country. And they went out to see what it was that was done. 15 And they come to Jesus, and see him that was possessed with the devil, and had the legion, sitting, and clothed, and in his right mind: and they were afraid. 16 And they that saw it told them how it befell to him that was possessed with the devil, and also concerning the swine. 17 And they began to pray him to depart out of their coasts.
The Mark author, in short, took the Egyptian pig fear river running phenomenon and sold it as a miracle of Jesus, to to bolster the touching-on-reality belief effect.
This "exorcism" of a legion of demons out of a possessed person into a herd of animals, seems to have found retold in the ending of the Peter Blatty's 1973 film The Exorcist, wherein the "legion of demons" inside of Regan passes into father Karras after which he plunges to his death (dereaction) out of the window into the cliff-like steps below.
The following are related quotes:
“The devils sent into the sea the bodies of swine in a country where no swine were kept.”— Voltaire (1764), Philosophical Dictionary (§:Christianity) 
“When, long ago, Thomas Huxley and William Gladstone debated the truth of the Christian religion in the pages of the Nineteenth Century, this great issue was found to turn upon the question whether the Gadarene swine had belonged to a Jew or a Gentile, since in the latter case, but not the former, their destruction involved an unwarrantable interference with private property.”— Bertrand Russell (1931), “Science and Religion” 
“So you believe that Jesus of Nazareth caused devils to leave the body of a madman and go into a flock of pigs, which hurled themselves down the Gadarene slopes and into the sea?— Christopher Hitchens (c.2009), “Question to William Craig” (Ѻ), Debate
1. Herodotus. (c.435). History of Herodotus, Volume Two (editors: Henry Rawlinson and John Wilkinson) (pg. 85). Publisher, 1875.
2. Gilgamesh, Horus and Tickheathen, Agnes. (2013). Awkward Moments Children’s Bible, Volume One (Foreword: David McAfee) (eB) (§:Delicious Demons, pgs. #) (Ѻ). CreateSpace.
3. (a) Voltaire. (1764). Philosophical Dictionary (§Christianity) (txt). Publisher.
(b) Joshi, Sunand T. (2014). The Original Atheists: First Thoughts on Nonbelief (pg. 54). Prometheus Books.
4. Russell, Bertrand. (1986). Bertrand Russell on God and Religion (editor: Al Seckel) (Amz) (pg. 179). Prometheus Books.