Revealing mistake: In the submarine, when Emma goes to get ice for Shaw, Azazel's tail is missing when he helps pull the submarine's ladder down.
Revealing mistake: Watch when young Charles meets young Raven. Look closely and you can see the zipper on the child actress' costume.
Revealing mistake: When Xavier saves Erik from drowning, the two have an exchange of words while floating at the water's surface. During these shots the water is churning violently around them but the two look stationary, indicating they are standing on a solid platform.
Chosen answer: Xavier can read minds, so it's assumed he knows about the murders.