Continuity mistake: 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. (00:17:45)
Continuity mistake: When David (in fact, he was Charlie that time) was looking for Emily in her room, he checked if she was under either of the two beds. After he bent down, he was checking the bed on his right side, but when he was shown from another camera angle, he was checking the bed on his left side, before he lifted his head again. (00:50:00)
Continuity mistake: When Emily is on the merry-go-round, she has permanent front teeth, but later in the film she still has baby teeth.
Answer: He keeps singing "mockingbird" over and over, but it is more of a mumbling by this point. Turn on the subtitles and you can see this.
EMTurbo