In the beginning of the movie, Tiana's dad writes "Tiana's PLACE" on the picture. At the end, the menu reads "Tiana's PLACE", but the restaurant is named "Tiana's PALACE". This deliberate name change is to emphasize the fact that Tiana is now a princess.
During the opening musical number, Big Daddy holds up a newspaper while in the car revealing a number of headlines including "Ford Corporation Introduces Trimotor" and "Gertrude Ederle Readies to Swim the English Channel." Neither of these events, nor Mardi Gras for that matter, took place on the newspaper's supposed date of April 25th 1926. The Trimotor first flew in June 1926, Ederle wouldn't swim the English Channel until August 6th, and Mardi Gras in 1926 fell on February 16th.
In the opening scene, someone on the streetcar is reading a newspaper with the headline "Wilson Elected" which implies the date is November 1912 (if it were 1916, the headline would have said "Reelected"). This contradicts the year on Big Daddy LaBouff's newspaper, and it also contradicts the time of year in which Mardi Gras takes place (February or March).
When Tiana and Ray were at the parole watching Charlotte and "Naveen" (Lawrence in disguise) about to get married, Tiana ran away in tears, thinking Naveen has betrayed her, even when she knew there was a fake Naveen, as she said when she first met the frog prince: "If you're Prince Naveen, who's that dancing with Lottie?".
During the song "Friends on the other side" Dr Facilier spreads the cards from right to left. After a cut to Prince Naveen's face the cards have switched directions as if spread from left to right allowing him to flip them over the way he did.
When Prince Naveen prepares the romantic dinner, he leans over the improvised table, and falls. However, only seconds later he gets up and sits on the edge of the table, which this time supports his full weight.
The first time the brunette and the blonde are seen clapping along with Naveen's performance, the brunette is wearing a lot of jewelry. However, the second time they are shown, some of the jewelry is gone.
When the frogs are at Mama Odie's they sit on the edge of the bathtub full of boiling gumbo without any problem. The gumbo is in an old fashioned cast iron tub and the edge would have been much too hot for them to touch, much less sit on comfortably,
Louis is established to be an alligator in the film. But when an alligator's mouth is closed, its teeth do not show out like a crocodile's. In the shots where Louis's mouth is closed, his teeth are showing.
On Mardi Gras, as the riverboat carrying Tiana and Naveen approaches New Orleans, the moon is full. This is impossible.
There are approximately 29 days between full moons. The date for Easter in Western Christianity is calculated as "the Sunday following the full Moon which falls on or after the equinox." Easter will always be at most 7 days after a full moon. Mardi Gras is 47 days before Easter, and will always occur 11 to 18 days after a full moon. Mardi Gras will fall within four days before or after a new moon.
In 1926--the year in which the film is set--Mardi Gras is on February 16, the new moon is on February 12.
Tiana is left-handed, but sometimes uses her right hand for writing and kitchen work. For much of European and American history, society considered using the left hand to be sinful or unnatural, so "lefties" often felt compelled to use the right hand in polite company.
On several occasions (particularly in "Almost There" and at the ball), there are numerous people either drinking or holding glasses of wine or champagne. This movie is set primarily in the 1920s. The possession and sale of alcohol in the United States was illegal between 1919 and 1933, because of the 18th Amendment (Prohibition), though Prohibition was widely disregarded, especially in New Orleans.
When Charlotte kisses Prince Naveen, and the spell doesn't work, Charlotte did not turn into a frog like Tiana did earlier, when she should have because she kissed him after midnight, which means she was no longer a princess of Mardi Gras.
When Tiana first becomes a frog, she asks Naveen if he was a frog, who did she see dancing with Charlotte so she knows there is a "fake" Naveen. Yet, when she sees the fake Naveen on the float with Charlotte, she feels Naveen has betrayed her and hops off. She should know that that is not really Naveen.
The newspaper at the beginning of the movie talks about Naveen's trip to the states and reports that the small obscure country sent their only son. At the end of the movie in Tiana's Palace Charlotte is dancing with Naveen's six and half year old brother.
After Dr. Facilier retrieves the talisman from Tiana he turns her back into a frog and pins her down with his cane. The cane is there but after she grabs the talisman with her tongue the cane disappears and is nowhere to be found.