This missing piece is all about Walt, but he’s not shown and his name isn’t even mentioned.
When it starts Juliet is standing in a corridor, and there are people rushing by with an alarm going off in the background. Ben approaches from the end of the corridor, and asks what’s happening, Juliet replies “he did it again”. Ben questions this, “did what again?”, Juliet says “you know”.
Ben tells Juliet that she’s going to have to ask him to stop doing it. Juliet refuses to go into the room, says no one else will go in there either because they are all scared. They talk about ‘him’ (Walt) and Ben says that it was Jacob that wanted him there because he’s special. Juliet disagrees, she says he’s dangerous. She takes Ben outside to show him something.
Once they are outside Juliet says “what kind of a child does this?” and shows Ben a ‘collection’ of dead birds on the staircase, just below a boarded up window which we can assume is the window to Room 23 where Walt is being kept. I suppose whatever “it” is that he’s doing is resulting in the dead birds.