Locke tells Ben that he will be killing Jacob

As the others are making their way across the island to Jacob, Locke asks Ben why he hasn't told Richard about his plan to kill Jacob. Ben says that he assumed Locke wanted to keep it a secret and Locke asks "When did that ever stop you?" Ben says that he started looking at things differently since Alex told him that she would destroy him if he didn't to everything that Locke said. Locke asks him when that happened and Ben tells him it was under the temple with the smoke monster.

Locke says "So you're willing to do whatever I say, no matter what it is?" In a defeated, quiet voice Ben says "Yes." Locke says that he won't have to convince Ben to kill Jacob then. Ben stands there with a depressed, shocked and defeated look on his face.

So fake Locke seems surprised that Alex spoke to Ben, so does this mean he is not an incarnation of the smoke monster or is he just playing dumb. It does seem weird now that Locke was gone the entire time Ben was surrounded by the smoke monster and talked to Alex. I guess this is something we're supposed to ponder for the next eight months.