Right after Charlie offers to go in and save Jack, he says, "Let me do this," and the camera cuts to a large, green, mountain type shot, and a fence is visible running across it.
In the flashback scene where Charlie visits his brother's home, the boom mic is reflected in the top of the window on the left side of the screen as Charlie knocks on the door.
The method Sayid refers to (triangulating) actually just requires two sensor locations instead of three.
The "cocoon" that Locke points out is a chrysalis. He then talks about how moths spin silk. They do this in order to make a cocoon, but, again, he points out a chrysalis, not a cocoon.