Revealing mistake: When Kate is on the phone complaining about the water being cut off, the iron overheats. Kate then runs over to it, and the shadow of a crewmember is cast on the iron and ironing board, then moves out of sight. (00:23:30)
Revealing mistake: When the Cherub grabs Ruthie and throws her into the shower glass panel, look very closely and the glass is all smashed before she even touches it. (01:09:15)
Revealing mistake: In the beginning of the movie when the medical examiner is about to perform the autopsy, if you look at the cadaver's stomach, you can clearly see that it is breathing.
Answer: He doesn't kill her because she was the only nice one, whereas her friends( Paige, Lily, etc.) were all mean to him at the beginning.
cameron_eats_lemons