Continuity: In a scene near the end of the movie, George enters the Building and Loan with a Christmas wreath on his arm. On hearing that he has a phone call from his brother Harry, he tosses the wreath on a table and picks up the phone. In the next second, the wreath is back on his arm.
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Mistakes
Harry Bailey's tombstone has the dates of 1911 and 1919 making him 7-8 years old when he died, but the angel states that Harry died when he was 9 years old. If he was born the latest at 31-12-11 and died 31-12-19 he would have been exactly 8 years. If he was born 1-1-11 and died 13-12-19 he would have been 8 years 364 days, one day short of 9. If he was born later than the day of the year he died he would have been 7+. See more...
It's a Wonderful Life mistakes
Continuity: In a scene early on in the film, where George Bailey (James Stewart), Bert (Ward Bond) and Ernie (Frank Faylen) chat in the street, they suddenly stop due to the appearance of Violet (Gloria Grahame) in her "this is what I wear when I don't care how I look" dress. The camera cuts back to them and we see a dark haired woman in a hat pass in front of Ernie's taxi. As Violet crosses the street, we see another shot of the boys staring after her - and the dark haired woman passes in front of the taxi again.
Continuity: When George Bailey crashes his car into the tree after leaving "Martini's Place", notice its position against the tree; an upward angle. In the ending scene when he's running home he cheers and taps the hood of the same car, now at a downward angle.
It's a Wonderful Life trivia
Many if not all of the wintry scenes were shot in a record breaking heatwave. It got so bad once, that Capra gave people a day off to recuperate.
The scene in the bar where Jimmy Stewart is crying and saying "please God" was originally not shot as a close up. Capra shot the scene, then asked Stewart to act the scene again for the close up shots. Stewart didn't think he could reproduce the emotion, so Capra actually blew the scene up frame-by-frame.