When Mary and George are walking down the street after the dance, she asks him at 0:24:46 (2007 DVD), "Well, why don't you say it?" The next shot George is heard saying, "I don't know. Maybe I will say it," but his mouth is not moving at all.
When drying off after his jump in the river, Clarence mentions his book, The Adventures of Tom Sawyer. He also mentions that George should check out what Mark Twain is currently writing. If he means 1945, the current year, Mark Twain wouldn't be writing anything, because he died in 1910. We don't know how he has the book. He couldn't have died with it like the night gown, because he says he's been waiting 200 years for his wings which would mean he died at least 131 years before it was published in 1876. Since Clarence is said to have "the IQ of a rabbit," and made a mistake regarding Harry's age in the sledding scene, and has apparently suffered multiple failures to earn his wings, he is likely confusing the date of his present assignment with a previous failed attempt to to assist peoples' lives on Earth in the past.
Due to his references to Mark Twain's writing and his outdated underwear, Clarence most likely died in the late 1800's, probably between 1876 - 1884, the publications of Mark Twain's two most famous novels. However, this does not square with his declared age in the bar; he says he will be "293, next May", which in 1947 would mean he was born in 1654 and therefore died in the early 1700's.
An uncredited actor wearing a dark turtleneck sweater in an unnamed role is the second boy to slide down the river bank. At 0:04:20 (2007 DVD) when he is halfway down the bank, a shout "Come on, Marty" can be heard on the soundtrack even though Marty (who slides third) is still standing at the top of the bank watching this second boy slide.
When Mary puts on "Buffalo Gals" on the phonograph at 0:43:38 (2007 DVD), she starts a ten-inch, yellow-labeled record, but in the next shot, a dark-labeled record is playing. Also, when Mary breaks the record at 0:46:46 after the conversation with George, she breaks a twelve-inch, yellow-labeled record instead of the original ten-inch record.
After Clarence disappears whilst being wrestled by Bert the cop at 1:56:26 (2007 DVD), you can see the shadow of Ernie the cab driver shaking his finger. However, when the camera shows Ernie, he has both hands on the tree, and then he begins to shake his finger.
As George approaches Bert and Ernie by Ernie's taxi, and then all three ogle Violet as she walks down the street, the same woman in a print dress, holding the brim of her hat, walks by five times in 30 seconds from 0:13:25 to 0:13:59 (2007 DVD).
As Violet walks away from George, Ernie, and Bert at 0:13:47 (2007 DVD), Ernie watches her out the window of his taxi. He stops watching and moves away from the window at 0:13:57. In the next shot, he is watching from the window again at 0:13:59.
When George is on the bridge at 1:38:46 (2007 DVD), the snow and ice pattern on his left coat shoulder is the same as it was when he was in Potter's office at 1:32:38, even though he was in the bar at 1:35:28 with no snow afterward.
During the run inside the Building & Loan, the hat changes position on the coat stand outside George's office. At 0:53:20 (2007 DVD) the hat is on top of the pole while at 0:55:09 the hat is on a hook.
When George has Mary's robe, the cord is trailing along the ground at 0:29:20 (2007 DVD), but when George pitches the robe onto the hydrangea bushes where Mary is hiding at 0:28:25, the cord is all bundled up.
When George and Mary are throwing rocks at the dilapidated house on the way home from the dance, as George throws his rock, the window that Mary is supposed to throw a rock at is missing. Then when Mary gets ready to throw her rock, the window is there.
As George and Mary prepare to drive Martini's family to their new home, Mary (in a close up) is holding the goat's horn. The scene cuts to an extreme long shot in which her hand is nowhere near the goat.
Dr. Campbell comes out of the Bailey Building & Loan board meeting at 0:34:32 (2007 DVD) to tell George the board voted down Potter's motion to dissolve the Bailey Building & Loan institution subject to one condition -- at this point, 0:34:42, the camera is focused on Dr. Campbell with Uncle Billy looking at George and the scene cuts to a shot focused on George but with Uncle Billy looking at Dr. Campbell who states the condition: that George accept his appointment by the board to become executive secretary.
When George visits his father in his office and finds him arguing with Potter, his father is standing behind his desk. At 0:09:44 (2007 DVD) the scene cuts to a close-up of Potter in his wheelchair carrying on their argument. At 0:09:52 the scene cuts back to the longer shot, but now Peter is sitting on the front of his desk, face to face with Potter.
When Potter talks to Billy at the bank, his scarf is clearly visible when Billy snatches away his newspaper at 1:19:21 (2007 DVD), but it is scarcely visible as Billy reads the headline aloud at 1:19:23 and is clearly visible as he tucks his glasses away at 1:19:34.
A hat being held by someone donating money in the Bailey house, first has a little snow, then a lot of snow, then no snow. At 2;06:53 (2007 DVD) a little snow is on a gray hat at left of screen as Ernie reads Sam Wainwright's cable; at 2:07:14 much more snow; at 2:07:20 no snow; 2:07:25 no snow; 2:07:32 no snow; 2:08:18 no snow.)
Alignment of George's car when it hits the tree. At 1:37:39 (2007 DVD) George has run the left side of the front bumper directly into the tree trunk. At 1:37:40 the trunk is to the left of the left front wheel. At 2:02:47 the trunk is still left of the left front wheel.
When George invites Carter to come in and follows him in, he is holding the pipe with his left hand. However, in the shot after, someone asks him about hanging up the phone, he appears with the pipe in his right hand.
Ma Bailey has lunch with Harry and President Truman on Christmas Eve, but she's back in Bedford Falls by the time Mary returns with the collected money, even though Harry Bailey shows up later having flown through a blizzard.
George Bailey is the first of the six boys on the top of the river bank to slide down on a grain scoop shovel. At 0:04:11 (2007 DVD), as George sides onto the river ice, a seventh boy is visible at the top-left of the frame sitting on a crate on the ice, but he is not visible as George slides across the ice and walks back. He is likely a vestige of a screenplay line, such as tracking who slides the furthest, cut during editing. He is also the one who trips over Sam's leg at 0:04:58 when the boys form a human chain.
In the 1919 summer scene when young George and Harry Bailey and four of their friends are walking down one lane of the boulevard, all with their arms interlocked, Harry Bailey is carrying a catcher's mask in his right hand at 0:05:11 (2007 DVD), but when they reach the drugstore Harry is wearing the catcher's mask at 0:05:29, even though their arms are still interlocked.
When Potter is offering George a job, as George stands and leans over Potter's desk, above Stewart's head and out the window appears to be a 'modern' vehicle (colored blue in the colored version) with a chrome door handle.
(at 2:06:07) (2007 DVD), 'The Bells of Saint Mary's" (1945) is playing at the Bijou Theatre. It premiered in New York City 12/6/1945, and was actually released 12/27/1945 to the first-run, big-city theatre circuit, and would not have been playing the neighborhood, small-town theatre circuit this early (Christmas Eve, 1945).
When Clarence is being told what is going to happen to George Bailey, he is told that it will happen "at 10:45, Earth time". However it will be 10:45 at some point that day all over the globe. Without a location being defined, Clarence would have to check the entire globe throughout the day! Even the contiguous United States have 4 time zones.
In some colorized versions, Ernie the cab driver is seen in the last scene wearing a light blue shirt with epaulets and an Air Force "flying star" shoulder patch. The Air Force uniform did not include light blue shirts until 1949, two years after it separated from the Army and three years after this film was made, and did not include light blue shirts with epaulets until the 1970s and in any case never authorized shoulder patches with any type of light blue shirt. As the Air Force was still part of the Army at the time, and based on the light shade, Ernie's shirt was presumably khaki in real life.
When Harry has his accident, he slides off the ice into a large area of open, moving water, not simply a small hole in the ice. Under these water conditions, the ice near the edge would be too thin to support the several boys already there.
When George Bailey is arguing with Mr. Potter in the board room after Peter Bailey's death, George says to Potter: "What'd you say just a minute ago? They had to wait and save their money before they even ought to think of a decent home." We never hear Potter say this, but it is possible that it happened near the beginning of the meeting, which we did not see.
The characters of cousins Tilly and Eustace DO NOT pose a problem. They are both Baileys being their last names are on their desk plates. These two, as well as George and Harry, all call Billy "Uncle Billy" throughout the film. It is further established that Peter Bailey is the father of George and Harry, with no mention of Billy having children of his own. However, it is never established that Peter and Billy were the only brothers in that generation of the family, nor the only brothers involved in the Building and Loan. (Presumably Tilly's and Eustace's father (or fathers) is/are deceased by the start of the story.)
Harry Bailey is not "shown jumping from a plane with other paratroopers". He is shown in the Ready Room of his aircraft carrier, (the walls and door of which are decidedly not shaped like the interior of a troop transport airplane) going through the exit to the flight deck to his fighter plane. He and the other fighter pilots wear padded cloth aircrew helmets with radio headphones and goggles, not "steel pots" like paratroopers would, and there is no overhead static jump line at the doorway to which paratroopers' parachutes would be hooked up to.
Supposedly, the $8,000 is still missing at the end of the film. While family and friends have provided George Bailey with additional monies at that point, if or when an audit is performed, he still has to explain what happened to the money that his absent-minded uncle lost. This puts him in the same position that he was before he received the additional donations/deposits.
In fact, without a solid explanation as to where the money went, it would likely be assumed that the money was either stolen by Uncle Billy or embezzled by George himself. The building and loan would likely face legal sanctions as would George Bailey.
However, cash is cash. The Building and Loan does not have to explain what happened to the specific bills that were lost; they simply have to have $8,000 on hand to keep the books accurate. For the same reason that George can use $2,000 of his honeymoon cash to keep the B&L afloat, he can take the $8,000 donated by the townsfolk to balance its ledgers.
In the drugstore when Mary leans over the counter to whisper in George's ear, a piece of tape suddenly appears on the edge of the counter between George's and Mary's heads at 0:06:59 (2007 DVD). This was most likely done as a reference mark for the young actors so the focus puller could accurately pull focus.
When Mary (Donna Reed) throws her rock at an upstairs window of the dilapidated old house, the rock disappears a split second after leaving her hand, and then reappears in the distance just before crashing through the glass. The roof of the house was a matte painting, added after principal photography by the visual effects department. When Ms. Reed threw her rock (and it was her throwing it, not a stand-in), the arc of its flight was a bit too high, and it crossed the matte line for most of its travel. Consequently, it was covered up by the painting, which was added later. Apparently the live-action crew did not notice the potential problem when filming the shot.
When Uncle Billy is counting the money at the bank for the deposit, we can clearly see the first few bills are 5's, followed by, at the most, 20 more bills. Considering that these would have been monthly cash payments on $6000 mortgages, it is unlikely that anything close to $8,000 could have been in that small stack of bills. It is about 1/3 of the size of the wedding money which is 1/4 of the amount.
In the montage depicting what happens to the townspeople of Bedford Falls during World War II, Joseph narrates, "Marty [Mary's brother] helped capture the Remagen Bridge," whilst Marty is shown calling out urgently and giving the classic infantry "Follow Me!" gesture. In the rear projection stock footage making up the background, however, American troops are actually walking casually onto the bridge in a non-tactical manner. The lighter-shaded rectangle on the right bridge tower is actually a sign that reads "CROSS THE RHINE WITH DRY FEET, COURTESY OF 9TH ARMD DIV.", which was put up the day after the bridge had been captured.
When the film makes the jump from 12-year-old George Bailey in Mr. Gower's drugstore to the adult George Bailey in the luggage shop, the character has clearly aged at least 20 years (Jimmy Stewart was 37 or 38 at the time of filming), but both his father and Mr. Gower appear not to have aged at all in the following scenes. They look the same as they did when George was 12.
The goof items below may give away important plot points.
On the tombstone, Harry Bailey's years of life are show as 1911-1919, which would make him, at the oldest, eight years old when he died. However, immediately before George Bailey brushes away the snow to reveal the dates, Clarence states at 1:58:42 that Harry died when he was 9, showing that Clarence isn't numerically inclined (or that actor Henry Travers cited Georgie Nokes' age during filming - Nokes played little Harry).
In the first scene where George finds his brother Harry's grave, the year of death (1919) is clearly visible. The next scene, it is obscured by snow and George has to dig it out to find the year his brother died.
Since George was a child when Harry died, then the cemetery where Harry is supposed to be buried was in business at least ten years before George could have bought the land to build the houses in Bailey Park .