When watching "LaFleur", I noticed Horace ordering the Arrow to break out the "Heavy Ordinance" and make sure the fence was turned up to maximum. This made me wonder: if the Others had obviously forded the fence, then why have the fence turned up to maximum? Then, it hit me: he wants the fence turned up to max *because* they're breaking out the heavy ordinance: the Smoke Monster. The fence was meant to stop it from backfiring on them. The fact that an entire DHARMA station was devoted to R&D against the Others meant they were working on something new, a weapon unlike anything which could be transported to the island. That means they developed something entirely new, based on their research of the island. The Smoke Monster, which has been confirmed to be unable to leave the ground, could be