Revealing mistake: The "movie set" steps were so steep they almost looked like they were flat against the wall and the handrail posts were so close together they looked more like vertical blinds. The little dog was able to scale the steps one-by-one, but the larger dog had to leap with effort to get to the top. Also, the baseboards on perpendicular walls (lower right-hand corner of the screen) were not in alignment (off by at least 1"). (01:11:54)
Revealing mistake: The man sitting at a sidewalk table perhaps 4' behind Henry was suddenly very close in back of him. (Use of a green screen). (01:17:24)