Season one! The Losties first get to hear the monster rampaging through the jungle, crushing trees. And when looking for the cockpit, we see the pilot getting eaten by it and Jack, Kate and Charlie get chased by it afterwards. Although, the actual "seeing" of the Monster doesn't occur until "Exodus, Part 2", where Jack and Kate get a brief glimpse of it before it attacks them, and again after it attacks Locke. An extremely brief glimpse can also be caught for a split second during Boone's vision in "Hearts and Minds." The first time we get to see it for an extended period of time is in "The 23rd Psalm," when it stares down Mr. Eko.