One fact that I want to recognize is that the hand the monster grabbed Eko with was long, and skinny (maybe like an orangutan?)
Important Note: In an effort to dispel misinformation, one important fact must be said about the Smoke Monster before anything else.
The Smoke Monster is NOT made of Nanobots. While this was a very popular theory, it has been denied numerous times. For those who need proof, this quote comes from the November 6, 2006 edition of The Official Lost Podcast (exact quote thanks to
Lostpedia):
Damon Lindelof (producer and writer): Ohh, nanobots. I don't know how many times you can you can go on record saying that the black smoke is not made up of nanobots before you stop getting asked that question. 
The smoke on
the island is a living, almost breathing entity and swirls around in the jungle tearing up trees, and generally striking fear into the hearts of the Islanders who encounter it. The smoke has made periodic appearances, starting in the fifth day on
the Island, when
Locke ventures in the jungle to hunt boar, and finds himself face to face with the monster. Later, during Season One, Episode 24 (
Exodus II), when
Locke,
Jack,
Hurley, and
Kate are carrying the dynamite they found at the Black Rock. As they carefully make their way back through the jungle, the smoke Monster descends upon
Locke and he falls to the ground. The Monster pulls him through the jungle and into a hole, and after a nasty tug of war
Kate releases the Monster's hold on
Locke by throwing dynamite down the hole. Before this whole chapter,
Danielle Rousseau said that it was
the Island's security system.
In Season 2, we get an even better look at the smoke Monster in Episode 10 (
The 23rd Psalm), when it actually develops a recognizable face.
Charlie and
Mr. Eko are in the jungle and
Mr. Eko has an encounter with the smoke and through it we see multiple images of his past.
After seventy-one days on
the Island, Eko is called to be judged by his brother, and while he's on the jungle the smoke appears near him multiple times, and almost engulfs him in the moment when
Locke arrives. After Eko refuses to confess to his brother Yemi, the smoke grabs him and violently murders him.
After John saw the monster, he told
Jack "I've seen in the eye of
the island, and what I saw... was beautiful". He then changes his attitude, and states that everyone was brought to
the Island for a reason - destiny took them there. When he asks Eko, on The Cost of Living, what he saw, he tells him that he saw a beautiful, white light. Later, prior to Eko's burial, he tells
Sayid that what killed Eko is the same thing that took them to
the Island, and that he was killed for a reason.

In
"Left Behind",
Kate and
Juliet encounter the Monster in the night. They hide in a tree, and then there are flashes of light (as if it is taking pictures of them). Later on, They see the Monster again. they go behind the sonic fence, and then
Juliet turns it on. The Monster comes, but is repelled by it.
Juliet says that it doesn't like the fence and that
iis all she knows about it.
So far the Smoke Monster has claimed several victims including:
The Pilot of the Plane
Mr. EkoTriviaSome people believe that the Monster is seen in the first episode when Gary Troup is sucked into a plane engine. Right after being sucked in, a black shape can be seen swooping from the sky and hitting the engine just as it explodes. It was later revealed by the producers that the black shape was used for special effects timing, and wasn't removed properly afterward.
The producers have also stated that The "monster" doesn't appear in the first episode at all.
Theories
- I think there are
two monsters , one good and one evil. The black smoke monster ( the evil) was Eko's brother and led him to his death. He could also be
Walt, since he led to the death of
Shannon. Both of these were mostly black apparitions.
As for the second monster( the good one) would be the one
Locke saw, since he describes it as a beautiful light. This monster would be helping the survivors by visions like Christian( he led
Jack to the caves).
- The smoke "creature" has the ability to take different forms, since in episode 5 of Season 3, "The Cost of Living", the entity that appears to be Eko's brother denies its identity as Yemi, leading us to believe that it was in fact the black smoke creature that had taken Yemi's form and lured Eko in the jungle. Furthermore,if this is in fact true then it would explain the appearance of people like Christian,
Walt, Yemi, Dave coming out of the jungle.
Producers have hinted that this could indeed be true. All of these appeared
characters had a purpose (Eko's confession, leading
Jack to the caves, trying to get
Hurley to kill himself, and warning
Shannon). It could have also taken the form of
Kate's horse and
Sawyer's boar; if you listen carefully, during the first scene of whispers in "Outlaws", you can clearly hear the monster, and even more once it's heard
"It'll come back around".
-Many people think that the monster took the form of Dave, but Dave was
Hurley's
imagination. Hurley's "Imaginary friend".
-
Juliet says in the episode that aired 4/4/07 that "BSM" it doesn't like the invisible security system
the others has set up. The same one that John threw Patchy in and killed him.
- The smoke "monster" is their fears and the bad things they did before the crash. In "The 23rd Psalm", Eko just stares at the monster and it goes away. Maybe this is a sign of him facing his fears and his sad past. I think that it taking the form of the people they knew is a sign of them facing their past again.
- The BSM has a definite mechanical sound to it, so I'm in with the idea that it's some sort of machine. One of the 'maps' of
the island refers to something called 'Cerberus', and I'm gonna guess that's the BSM. "Cerberus" is a 3-headed dog that guards the Underworld in Greek
mythology. And we can actually see the 3 faces when the smoke monster faced
Mr. Eko in Season 2.
- If you listen closely, when the monster is whipping Eko around, there is a distinct sound of machinery, almost like a roller-coaster that's starting up a hill. It's possible that the black smoke is some sort of machine.
- Here is something that I discovered. The smoke monster closely resembles Cynothoglys, the Mortician god. I do not know how factual this information is, but if you want to read more about it go to
http://antediluvia.pbwiki.com/Cynothoglys. After you read this, you will find many similarities between the two.
- I'm not sure what the smoke really means, but at the top of this page, it says, "the hand the monster grabbed Eko with was long, and skinny (maybe like an orangutan?)" On
the Hanso Foundation site, it showed a life-extension project, of an orangutan named Joop, who turned 105. Perhaps there is a connection.
What does the smoke mean? Share your theories!
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