Plot hole: In the end, when Charlie is advancing on Emily while turning his light on and off, the final time he turns it on, Kathrine is in front of Emily. How could she get there so fast without being heard? There's at least 4-5 inches of water that would make sneaking very hard.

Continuity: When David is writing about Emily needing more time, etc. you see three lines in the close-up of him writing. When he picks up his hand and notices the spot on his palm there are 5 lines of writing on the paper.

Other: When Robert De Niro first tries opening Emily's window, it is closed and doesn't budge. Yet, you can see the curtains blowing anyway. The window is closed, so the wind should not be blowing into the room.

Continuity: When Emily is on the merry-go-round, she has permanent front teeth, but later in the film she still has baby teeth.

Revealing: Katherine shoots Charlie twice to kill him at the end of the movie. Yet if you look at the chambers on the side of the gun, you can see all of them are empty.