Question: What is the Monster?
The idea of a monster was introduced in Episode 1x1, Pilot Part 1.
Answer: There is something that lives in the jungle that the survivors call a monster. It makes loud clanking sounds and sometimes appears as black smoke. It killed the pilot of Flight 815 (Ep: 1x1, Pilot Part 1), tried to take Locke (Ep: 1x24, Exodus Part 2), and killed Eko (Ep: 3x5, The Cost of Living).
The monster dragged Montand to it's hole and as Jin and the members of the French science team held on to him, his arm came off and the rest of him was dragged into the hole. He said he was down there and needed help and that it was gone, so Robert and the other members of the team went into the hole to get him, but Jin made Danielle stay out because of her pregnancy.
Later, Robert told Danielle that the monster was just a security system guarding the temple (Ep: 5x5, This Place is Death).
