Revealing mistake: Ariel swims underwater and opens a book with stiff and easy-to-flip pages that produce a flutter sound when turned. The paper should be either soggy, or with its pages stuck together or even dissolved, and in no case sound and look as if it were dry.
Revealing mistake: When the Barrys cross through the glass door, for a couple of shots, Young Barry's face is replaced with a non-realistic CGI face with features that don't match the face contour at all.
Revealing mistake: Nick is supposed to play the saxophone, and his cheeks are puffed full of air, but they do not move at all. Playing the saxophone requires blowing into the mouthpiece, which moves the player's cheeks, mouth, and lips. (00:57:00 - 01:06:55)