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)
Continuity mistake: The changes/inconsistencies in how the lobsters were arranged on Frank's and Hildy's plates cannot be accounted for based on their movements while eating/cracking them open. (00:59:35 - 01:00:37)
Factual error: Tree foliage was unseasonal and inconsistent throughout the movie. For example, Autumn foliage (orange/yellow leaves) was shown, followed by a shot of a tree with Summer foliage (green leaves), then back to Fall leaves when Hildy was on her way to Thanksgiving dinner. At times, trees still had Summer foliage around Christmas time. By November in Massachusetts, trees would have few, if any, leaves on them (and they would not be green). (00:42:50 - 01:05:20)
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)
