In the second "Einstein on the Beach" scene, Mrs. Peterson's cocktail has a green umbrella. But when Sherman and Penny call Mr. Peabody, Mrs. Peterson's glass has a pink umbrella in it. Then, in the shot over Sherman's shoulder, when Mr. Peabody jumps down from his chair, Mrs. Peterson's umbrella is green again.
Inside the Trojan horse, after a comment about the smell is made, Agamemnon raises his arm to show his hairy armpit. But a few seconds later, and for the rest of the movie, he is shown to have hairless armpits.
Ms. Grunion keeps switching seats inside the police car while chasing Mr. Peabody, being in the driver's side or the passenger side at various different scene changes.
The sewer cover falls into the tunnel and knocks out Robespierre. Round sewer covers can't fall into the hole they cover, since the hole diameter is smaller than the cover diameter, and can't fit it - regardless of its position.
Leonardo is shown painting Mona Lisa on canvas, but the real painting is a plank of poplar wood. While the movie often plays historical inaccuracies for laughs, this one appears to be unintentional.
In the Paris sewer Mr. Peabody asks Sherman if he smells anything. Sherman says he smells methane, but methane is odorless to humans. It's not clear whether a dog could smell it but Sherman certainly wouldn't be able to smell it. Commercial methane is given a distinctive smell so that leaks are detectable by humans because the naturally occurring gas has no odor.
The taser weapon is shown electrically arcing to shock its targets. Taser weapons can only shock through direct contact with the weapon or with electrodes fired from the weapon. Arcing is not seen.
Queens of ancient Egypt were not killed to join their deceased husbands. In fact, Tutahnkamun's widow is believed to have married Ay. From that point she vanished from history.
When Peabody demonstrates a "pratfall," he falls forward onto his face. A pratfall is specifically a fall backwards onto the buttocks, "prat" being an old English term for that anatomy. Regardless, this is a generic term for a humorous fall.
Early in the film Sherman says that the Leaning Tower of Pisa didn't always lean (suggesting that he caused it to lean). In fact the tower of Pisa has always leaned ever since it was built, due to a design flaw in the foundation. But this is an in-joke regarding the events of Galileo (1963).
Mr. Peabody and Sherman escape from the French Revolution in the sewers. Although early systems existed in Paris since the 1300's, that particular network of vaulted tunnels has not built until Napoleon's regime. In fact, at the time, Paris was notorious for its lack of sewers. and proper waste disposal.
The Reign of Terror is shown beginning in 1789, immediately after the raid on the Palace of Versailles. In fact, the Reign didn't begin until 1792.
In this film, the Reign of Terror is depicted as having started in 1789. This phase of the French Revolution actually lasted from 1793 to 1794. The de facto government of France in this period was the Committee of Public Safety (March 1793- October 1795), which was charged "with protecting the new republic against its foreign and domestic enemies".
The film depicts Maximilien Robespierre (1758-1794) as being already in power in 1789. While Robespierre was elected a member of the Estates General of 1789, he did not hold any senior executive office until 27 July, 1793.
Mr. Peabody is seen playing the trombone but the sound we hear is from a trombone with a straight mute attached to it yet Mr. Peabody has no mute in the bell of his trombone.
Agamemnon dubs Sherman as "Shermanus," which sounds more Latin than Greek.
At the time Jackie Robinson was playing in Major League Baseball, the Brooklyn Dodgers did not have player names on the back of the team jersey.
Leonardo is referred to several times as "da Vinci". Leonardo Da Vinci had no surname in the modern sense and would not have been referred to in this way by his contemporaries.
The actual Mona Lisa had no eyebrows, as it was in fashion to shave them. In the movie you can see she has eyebrows.
Mr. Peabody commits the offense of Failure to Yield the Right of Way when the stoplight turns green. A vehicle making a left turn has to yield to oncoming traffic at a single green light.