Just prior to his hanging, Blackwood is told he has been sentenced to death for "the practice of black magic". British law has not recognized magical acts since the Witchcraft Act of 1735. The only prosecutions have been against those who commit fraud by pretending to cast spells.
Following Holmes' leap from the House of Parliament, a statue of Queen Boudicca can be seen at the end of Westminster Bridge. The statue was erected in 1902, 8 years after the opening of Tower Bridge, which is partially built in the film.
Holmes describes the devices used to kill one of the villain's opponents and torch the abattoir as "employing a flammable substance." "Flammable" entered the language in the early 20th century, as a disambiguation of "inflammable," which means the same thing, but was mistaken for its antonym, "non-flammable." For safety reasons, it became preferable to use "flammable" when giving warnings about combustibility.
During Irene's first conversation with Holmes, she says she brought dates from Jordan. The country of Transjordan was established in 1921; the name changed to Jordan in 1949. Although, the name "Al-Urdun" (Jordan) was used on Umayyad post-reform copper coins beginning in the early 8th century, in 1890 the name Jordan did not appear on maps to represent the land of modern Jordan and would not have used other than as the name of the river Jordan. The land today known as the country of Jordan was labeled on maps of the era as Gilead or Bashan.
One shot of the Clocktower of the Palace of Westminster (commonly known as Big Ben) shows Portcullis House, the UK MP's offices, with its distinctive chimney stacks, to the right. Portcullis House was built in 2001.
Early in the film, Holmes reads a Daily Graphic dated 13 November 1890. The front page features a report of Blackwood's impending execution, accompanied by photographs of Blackwood, Holmes, and Watson. The Daily Graphic was the first newspaper to print a halftone photograph, but it started in 1891.
At the end of the restaurant scene, in which Holmes analyzes Mary, who leaves in disgust, Holmes uses a knife and fork to cut up and eat his meal. He holds the fork vertically between thumb and index finger, American-style.
Holmes sniffs a bottle of an unknown chemical by sticking his nose in an taking a deep whiff. The safe way to smell chemicals, which has been practiced for over 200 years, is to use the hand to gently waft the fumes towards the nose. As a man with some background in chemistry, Holmes would surely have known that.
During the meeting of the secret order, Lord Blackwood states that they'll execute their plan to take over parliament "tomorrow at noon". However, the next scene where Holmes examines the dead body leading to the confrontation at the slaughterhouse clearly takes place the following day and the confrontation the following night. Therefore, the order's plan doesn't actually take place until the day after 'tomorrow'.
When Blackwood talks to Ambassador Standish at the secret society meeting, he says America has been weakened by its recent Civil War. The Civil War ended in 1865, and the Reconstruction was over by 1877, so by 1891 when the film takes place, America was hardly in a weakened state.
When Holmes, Watson, and Irene are in the attic and Holmes is explaining the crime, Irene kneels to the ground to put a candle down to flatten out the map. In the next shot, she puts the candle on the map again.
When Holmes and Watson are taken to Lord Blackwood's slaughter house, they both jump from the Lucy into the shallow water near shore and make their way to the building. In the very next scene, their clothes are dry.
During Adler's first fight scene, a handkerchief is on the ledge. Holmes goes to look for the owner, is punched, spins around, and falls to the ground. The handkerchief is missing. When he stands back up, the handkerchief is back.
When Holmes performs the magic ritual he cuts his fingers on a sharp knife to drip blood in middle of the circle. The next morning when talking to Watson and Irene, there is no sign of trauma to either of his thumbs.
When Holmes is in the boxing ring, he spots the handkerchief on the railing. While he is looking around the ring to spot the owner of it, he takes a hay maker to the head and goes down. As he is dropping, the handkerchief disappears entirely then reappears as he is coming up again. It should be noted as well that the handkerchief in question is visible prior to Holmes spotting it.
During the bare-knuckle fight scene, Holmes gets a cut on his left lower lip. There is blood from it on his shirt when Watson comes to get him to meet Lord Blackwood before the execution. In the next scene, when Holmes and Watson are on their way to the prison, there is no sign of the cut on Holmes lip. Yet it is clearly visible in the prison scene that follows.
In the first overhead shot of street traffic, vehicles are driving on the right. The rest of the traffic shots show them driving on the left. The wide shot showing the streets of London shows two barouches driving on the right side of the road. In the UK, traffic travels on the left side.
The movie continues the common mistake of identifying Holmes' house as 221B Baker St. The house should be 221; "B" refers to the fact that Holmes lives on the upper floor. Mrs. Hudson lives at 221A Baker St.
The scene in the House of Lords shows a very large chamber, with lots of people, many standing behind the Lord Speaker on the Floor of the House, talking to each other until Lord Coward, the Home Secretary calls for their attention. In reality, the Lords' Chamber is fairly small. Peers must sit on their respective benches; they are not allowed to stand on the Floor of the House. The Speaker calls the House to order, not individual peers. In fact, as a government minister, Lord Coward would normally address the Lords from the government dispatch box, which can be seen on the Table of the House. Incidentally, the Table itself is incorrectly placed in front of the Lord Speaker. It should have been placed further down, with the Law Lords sitting between the Lord Speaker and the Table.
Although Sherlock Holmes refers to the book of Revelation as "Revelations", it is noted by Watson in the Sir Arthur Conan Doyle novel "A Study in Scarlet" that Holmes' knowledge was limited to what he found relevant to his detective work, and in fact that he had very little knowledge of literature or philosophy.
In Reordan's laboratory, Holmes says he smells candy floss. Candy floss (a.k.a. cotton candy) wasn't available to the general public until 1904, but it was invented in the mid-18th century. Holmes was often employed by wealthy people, so he could've had it before.
In the slaughterhouse, the dead pigs are transported straight from the flaming to the band saw. When the band saw cuts them apart, the pigs are hollow, with no internal organs. However, near the end of the movie during Holmes' elaborate explanation of the conjuring tricks, he explains that the stomachs of the pigs were the experimental subjects of a cyanide poison. It is possible the pigs were cut open or the organs were dissolved in the experiments.
In the film, 221B Baker Street has 3 steps to the front door. Modern-day 221B Baker St. has a street-level entrance. In Sir Arthur Conan Doyle's day, the address was fictional, and thus has no "real" representation.
When Sherlock Holmes is experimenting with the effects of music on flies, he mentions that the flies fly in an organized fashion when he plays "atonal" clusters. While "atonal" was first used to describe music written around 1908, by composer Arnold Schönberg, composer Franz Liszt's 'Bagatelle sans tonalité' was written in 1885.
When fighting Dredger with the hammer at the boat dock, Holmes stumbles over one of the very large dock chains and moves it several inches, revealing it to be made of a lightweight material instead of iron.
After the case is closed, Lord Blackwood's machine is taken by the "Secret Service". While there was a Special Branch of the police, the military intelligence Secret Service Bureau wasn't created until 1909.
The first few shots of the cemetery, where Blackwood was buried, were shot at a different time than the subsequent shots. Initially, the shadows are almost parallel to the length of the road. In later shots, they're at an acute angle.
In the slaughterhouse scene as Holmes and Watson free Irene before she is sliced by the band saw, clearly she is shown being saved by Holmes' quick hand. In the very next shot it shows Watson pulling her up and Irene thanks Watson for saving her.
Lord Blackwood's execution is done American-style. In Britain, the hood placed over the condemned's head was white, not black. The rope was not the coiled noose of western movies; it passed through a simple eyelet.
Even though Sherlock Holmes did not witness Standish's murder, he was still able to describe it presumably because Inspector Lestrade, who was both a member of the secret society and also held Holmes in his confidence, related what he had heard of the event through his secret channels.
Holmes says Blackwood faked his death using an extraction from a flower which is "quite infamous in the region of Turkey bordering the Black Sea for its ability to induce an apparently mortal paralysis." The modern Republic of Turkey was founded in 1923. However, in the 19th century, Westerners commonly called the Ottoman Empire "Turkey" and all of its inhabitants "Turks", even those that weren't ethnic Turks.
Although it is widely believed that British Peers (such as Lord Blackwood) were hung with silk ropes rather than hemp, this is likely a popular myth. The last Peer to be executed in England was Earl Ferrers in 1760. There is no evidence that he was hung with a silk rope, and nothing in law or practice suggests this would be the case over 150 years later.
Lord Blackwood was executed by hanging, yet when Dr. Watson declared Blackwood dead, there were no bruises, ligature marks on the neck, or dislocation of the cervical vertebrae. Absence of these traumas from hanging should have aroused Watson's suspicion.